I just wanted to get involved with what's going on here, in an attempt to be helpful.
I upgraded to 2.05 without a hitch, other than needing to reinstall my MODs.
I've read through some various posts, and all of the pages of this so far, and I'm not understanding when or how these specific errors developed for you all.
The best thing to do, is retrace your steps, possibly remove any MODs, or do a CLEAN install of 2.05.
By CLEAN I mean unzip your 2.05 zipfile in a temp directory, delete the config.php file, and the install and contrib directories, then copy the whole lot over to the directory your forums are installed in, overwriting all files.
Note, if using a template OTHER than SubSilver, this will NOT affect your template.
Note, if any MODs are installed, they WILL need to be reinstalled, with great care taken to fix any differences between 2.04 and 2.05.
That is the best recommendation I have for you after reviewing this thread.