2
Time for some more debugging...
If you can get to your administration area, go to System Admin - Preferences - General Settings and set the debug mode to 'Smarty Templates Debug', then save your settings. Go to your main page. You should get a new window (enable pop-ups if you don't) with the smarty debug information. Scroll down the page until you see '{$xoops_rootpath}' and note the value there. It should match what is in your mainfile.php.
Now, go to your admin area again and click on one of the modules you are having difficulty with - when the smarty information comes up, look again for {$xoops_rootpath}. Compare with your first result. If it differs, you probably have a similar situation to your earlier problem - XOOPS_ROOT_PATH is being defined in another location and is causing this problem. If you have a local copy of your site, you can easily search for "define('XOOPS_ROOT_PATH'" in all your files and folders. Also, look for additional copies of mainfile.php on your server, especially if you have attempted multiple installs