so-called "blank pages" in Xoops are caused by an error which terminates the script early. The goal of this page is to help you turn some debugging features on so you can get a more meaningful picture of what is going wrong, preferably some error messages. Please keep in mind, there is always an error which is causing the "blank page -- it may just be hard to get at.
You will not get a response in the forums if you just type "Help me, I get a blank page" because there is no way for anyone to tell what is wrong. If you can also give a list of the error messages you see, your chances for solving the problem are much better. (Also don't forget to specify which version of xoops you are running, whether it was an upgrade from a previous version, also your versions of mysql, apache/other webserver, PHP, and which theme and template set you are using. If you are using a lot of non-standard modules, it would be a good idea to list those too.)
A: To turn on debugging try the following things:
1. If you can get to admininstration menu, go to Preferences, select 'Main', and find the section on debugging options. Choose "PHP Debugging"
2. If you can't get to the administration page, but have access to mysql, try the query "UPDATE xoops_config SET conf_value=1 WHERE conf_name = 'debug_mode'". Be sure to make sure "xoops_config" matches the name of the config table in your installation. (NOTE: This does not work with XOOPS 2.2, see 2a)
2a. In XOOPS 2.2, go to your site's root file "recovery.php" and set the debug settings through the interface here
3. If you can't get to the administration page, and don't want to mess with mysql, but don't mind messing with PHP, then edit the file "include/common.php". Near line 83, change "error_reporting(0);" to "error_reporting(E_ALL);".
4. If this still doesn't work, your server or hoster may have turned off debugging in "/etc/php.ini" (linux) or "WIN_DIRECTORY/php.ini" (windows). Make sure there is a line in there "display_errors On".
5. If you don't have access to change this file (e.g. on shared hosting), then if the server uses the "apache" webserver, you can create a file called ".htaccess" to override the settings locally. This file should contain the line: "php_flag display_errors on". The tricky part is WHERE to put this file. Look at the URL you are having problems with. Put the file in the corresponding directory. e.g. If it is "someplace.com/xoops/" or "someplace.com/xoops/index.php" then you need to put the file in the main xoops directory. If it is something like "someplace.com/xoops/modules/system/admin.php" then put it in "modules/system" subdirectory of your xoops installation. etc.
B: Common Error Messages (and fixes)
Once you produce an error message you can begin to diagnose your particular problem. Generally you can ignore any 'Notice' or 'Warning' that you see. Be on the lookout for 'Fatal Error' as this is the most important one.
If you have been unable to produce an error message, proceed to section "C: Possible Fixes" and you can try some of the suggestions there.
Following is a list of error messages that you might see, along with steps you can take to remedy the problem. (Please feel free to add to this list, or correct the message so it more accurately reflects what PHP says.)
1. "Failed opening required..." or "Undefined function..."
This most likely indicates that a required file could not be loaded. First check if the file is there and in the correct location; if it is, then check the permissions of the file to make sure the webserver can READ it. It is also possible that the file is corrupted, or that your FTP program changed file/directory names. Check your FTP program settings (make sure you "preserve directory structure", and do NOT "force lowercase", etc...) and try again installing/uploading the files again.
2. "Call to a member of a non-object"
Very frequently this is caused by failure to connect to the database. If you get this error occurring near line 286 in kernel/configitem.php, then the database is to blame. Check your database settings in mainfile.php, and also make sure you have setup mysql permissions correctly, and that the database is actually running. In particular, try and access the database directly - if possible using the same user/password that you specified in the Xoops installation. Note that after you change permissions for users within mysql, you must perform "flush privileges" and/or restart your database server before the new settings will be applied.
This error can be caused by other problems as well. If you know PHP, check that file and line number and see which object is the culprit. e.g. If you see "$xoopsDB->query('blah');" on that line, then $xoopsDB is not an object, indicating the the database was not successfully connected. You may have to do a little digging to solve these problems.
3. "Cannot redeclare class ..."
The most frequent cause of this error is the installation of non-standard modules. Some modules are still in very early stages and have not been fully adapted to xoops 2 or have not been properly tested with xoops 2 and with other modules. Probably the module author has used "include" where she/he should have used "include_once". Usually the file identified in the error message will indicate which module is at fault. This module can then be deactivated.
* Or you can go to the line # specified and change the line from include('yourfile'); to include_once('yourfile'); - ackbarr
C. Possible Fixes (Compiled off of the XOOPS Forums)
Below is a list of various methods that have corrected the issue for different users on the XOOPS forums. Which one, if any, that will work for you is highly dependent on your particular installation. The list is not intended to be followed in order, but rather you should focus on what seems most relevant given your error message.
 In the php.ini, make sure that register_globals=on. You can check this by creating a test script with this single line of code:
NOTE: The XOOPS core should work without changing this to ON, but some modules may not and thus will give blank pages. Turning on the debugging options outlined earlier in this page will help you track down which section or module is causing the error.
 Sometimes the PHP GZIP module is not added or correctly compiled with PHP, go into the XOOPS admin (system>preferences) and turn off support for GZIP.
 Make sure that you have installed XOOPS according to the installation directions by CHMODing the cache dirs on a UNIX server.
 Re-upload the theme files for whichever theme you're using. Sometimes things get corrupted via FTP upload. First upload phpkaox and set your system preferences to use this theme.
 Make sure that your running PHP 4.12 or later (preferably 4.22 due to security fixes in PHP)
 Make sure that you dont have another CMS interferring with XOOPS like PHPNuke, PostNuke, etc.
 Make sure that the cache, uploads, templates_c directories are CHMOD 777 (anonymous r/w permission on Windows)
 Try turning Safe Mode off on the server. (Not recommended as it is less secure).
 Double-check the following permissions:
755 - all directories which dont require writing from the web server
777 - all directories which do require writing from the web server
644 - all files which dont require writing from the web server
666 - all files which do require writing from the web server
444 - mainfile.php
 Try switching to the default theme. Several themes are meant for xoops 1 or have not been properly converted to xoops 2, causing a variety of problems. If this fixes your problem, at least you've identified the source of the problem. If you find a problem with a theme, please post on xoops.org forums and/or notify the author of the theme.
 Try disabling all non-standard (i.e. anything not included with xoops download) modules. If you cannot get to your admin menu, you can do this by editing the xoops_modules table via mysql or phpmyadmin. Several modules are in early stages and have not been properly tested with xoops 2, sometimes causing problems. If this fixes your problem, try re-enabling one at a time, to determine exactly which module(s) are causing problems. If you find a problem with a module, please post on xoops.org forums and/or notify the author of the module
 Added by carnuke ... if http://mysite.com/user.php
returns a blank page, see this FAQ here
 Check if mysql extension is loaded in php.ini:
--- Additional details submitted by Max-Realms
on 2005/3/26 1:06:34
In my case, I got blank pages without debug errors showing. After a while of troubleshooting, I found that my database "user" had exceeded max_questions (50,000 per hour).
My server is hosted, so I can't change anything there. However, I found that if I created several more database users and gave them each full access to the xoops database, this problem was fixed. I don't know anything about Mysql, but perhaps when a db has multiple users, they share the load.
If this is in fact true, then it would be great if the mainfile.php and/or core files could be setup to skip to the next available database user when the default one exceeds these limts.
--- Additional details submitted by GlaDiaC
on 2005/7/25 14:34:04
Are you using your cpanel X File Manager?
cPanel X's File Manager module seems to add trailing carriage returns at the end of the PHP file (after the !>). You need to edit your PHP files some other way and upload them, or re-edit the file remove the extra lines. See this FAQ