When I try to add a center-column block on my homepage with the recent comments I get this fatal error with php debug switched on:

Fatal error: Call to a member function on a non-object in /home/oilsjter/public_html/gent/modules/system/blocks/system_blocks.php on line 381

Debug switched off shows a blank page.
I'm using 2.2.2 without hacks.
Any hints to solve this?

One or more comments are connected to a module that either has never existed or has been uninstalled.

How this happened, I can't really say, but if you can, then load up the xoopscomments table in a tool like phpmyadmin and note down the com_modid for the 10-20 latest comments (highest com_id)

Then look in the modules table and see if any of the noted com_modid's are not present in the modules table's mid column. If you find one (or more) delete the corresponding rows in the xoopscomments table.

Thanks Mith!
Because of a re-install the sequence of modules was srewed up, so the xoopscomments wasn't compatible anymore.
Great job!