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.