OMG, another bug grrrrrrr

Today I noticed one of my older (and inactive) websites had Authorization pop-up while requesting it via browser... Okay, lots'a closed threads on this forum about this, so I started reading...
v7.5.4 hotfix? check
v7.5.5 update? check
cmd> websrvmng.exe --update-anon-password --domain-name=<domain>? check
ftp password reset via CP? check

hmm... still not working :\

"Permissions check-up" in "Domains"? error

SCREENSHOT

Note:
I cannot access ANY website via CP anymore... it stucks on this screenshot, and if I click OK it redirects me back to domains list.
I posted this while waiting for SWsoft reply (which I hope it wont be "give us permission to access your server")...

Update:
None of my clients can access their CP

Latest update:
As SWsoft support were insufficiently helpfull and wanted to charge me for resolving their own bug, I decided to back-up everything (via Plesk Backup), went to Control Panel -> Add/Remove Programs -> Plesk 7.5.5 for Windows -> Change -> Repair and after ~20 minutes of praying that everything goes okay, the thing works! All settings intact... phew... was starting to get greys