I "sort of upgraded" from XOOPS 2.0.7 to 2.0.18 and have following ERROR when trying to save changes on admin page for groups on modules/system/admin.php?fct=groups&op=modify&g_id=1

Error:
Notice: Only variables should be assigned by reference in file /modules/system/admin/groups/main.php line 70

Upgrade to 2.0.18 was done by installing 2.0.18 in new directory and new db. Then I "sort of added/replaced" all files - that were not present in 2.0.18 - from old system 2.0.7 and transferred content of databse in new 2.0.18 db.
I did not implement any upgrade files.

Problem is, that module article management system (AMS) does not show, even it is installed all right and on modules/system/admin.php?fct=groups&op=modify&g_id=1 the privileges for module AMS are set all right. But when I try to save privileges, the error shows up: "Notice: Only variables should be assigned by reference in file /modules/system/admin/groups/main.php line 70". When I call admin.php for groups again, the privileges are still set, but AMS just does not show up.

As 2.0.18 is running with less errors thean 2.0.7 I'd like to find a solution for this problem, because I need AMS module.

The reference error is fixed in 2.3 SVN.
http://xoops.svn.sourceforge.net/viewvc/xoops?view=rev&revision=1403

But I don't think that's the cause to your problem.

I downloadedhttp://xoops.svn.sourceforge.net/view ... ps?view=rev&revision=1403

but now I get Error "Access Denied" when calling ../system/admin.php?fct=groups (../htdocs/admin.php is still o.k. with user admin).

Do I have to adjust the downloaded system/admin/groups/main.php file?

I will try to find more specific errors and try to do the "official" upgrade (from 2.0.7) to 2.0.18 ...

thanks for the first shot with system/admin/groups/main.php.

Modify the file manually around line #70

Chnage
$group =& $member_handler->getGroup($g_id);

To
$group = $member_handler->getGroup($g_id);

more errors that might be related to "main.php line 70
" when trying to edit and save group privileges as described above

just calling system/admin.php?fct=groups (not trying to edit and save).....
.... shows following errors:
Notice: Only variables should be assigned by reference in file /modules/system/admin/groups/groups.php line 45
Notice: Only variables should be assigned by reference in file /kernel/module.php line 550
Notice: Only variables should be assigned by reference in file /kernel/module.php line 550

... found XOOPS posting on error "module.php line 550 "
https://xoops.org/modules/newbb/viewtopic.php?topic_id=62964&forum=4&post_id=283575
... where you advised:
You may change php.ini -> should I try?
allow_call_time_pass_reference = On
or check SVN:
http://xoops.svn.sourceforge.net/view ... ps?view=rev&revision=1290

Maybe I have a PHP-version problem?
PHP Version on surpass is only 4.4.6 -> is that a problem?
local PHP is OtSTriad 1.4 - Apache 2.2.2/PHP 5.1.4
php-version problem because when I login with admin locally administration menue is not displayed -> just loops back to startsite -> that happens with existing 2.0.18 dir run against a newly installed db.

I changed from
# $group = $member_handler->getGroup($g_id);
to
$group = $member_handler->getGroup($g_id);
and still get Error Access denied -> as both lines have same syntax.

the syntax "=& xoops" I only find 1 line above in: $member_handler =& xoops_gethandler('member');
... but that is different from your advice (I removed the "&" there as well but still same error)