Strange behavior when logging in

Hi!

My site (planetoidi.com) is running strangely. Whenever I log in, getResources stop working and the entire site starts acting up (menus not expanding, getting error 500s). I even rolled back to 32 hours earlier snapshot. This kind of helped: now my site is up, but the moment I log back in, everything breaks. If I copy the cache directory from the snapshot, I get the site back up again. I thought that the issue is same as here: https://forums.modx.com/thread/?thread=78611&page=2 but I'm not sure anymore. Oh, and the error log from snapshot was 12MBs in size! It repeats this over and over again:

[2012-11-18 17:56:28] (ERROR @ /index.php) Could not get table name for class: modFileMediaSource

This happens when the site is functioning "normally"

This is so confusing I'm having hard time even properly documenting the error.. happened so far:

1. The error mentioned above can be found in error log as far as month back, so this is happening all the time
2. Logged in today -> everything came to a grinding halt, first symptom was the getResources not working
3. Tried manually emptying the cache, no effect. On the contrary, menus started acting up.
4. From php error log I get following:

[23-Nov-2012 09:34:09 UTC] PHP Fatal error: Class 'modContext_' not found in ../core/xpdo/xpdo.class.php on line 761

5. Rolled back to 32 hours ago (DBs not rolled).
6. Refreshed the site, works fine. Logged back in, same behavior as in phase 2.

Any ideas?

Oh, and now my ModX error log is filling up with caching errors. I've tried setting the cache directory to 777 and to 755 to no avail.

Forgot to mention my ModX version, it's 2.2.5-pl (traditional)

Could you tell us more about the hosting environment, also have you tried uploading a fresh install and running upgrade again, incase you have a missing/corrupt file?

Could your site be close to its file storage limit? If it's having problems trying to write to and update the cache files due to running out of space, that could be causing this problem.

I haven't tried a fresh install, I suppose that's the next step Storage limit is no issue, I have half a TB available.

Hm. All of the sudden everything seems to be working fine. I haven't changed anything. Now 12MB size error log is still filling up with caching errors though.