Since just now, I found that I have to start Miranda as an administrator. I enabled UAC on my pc, and that's when this started surfacing. Strangely, even after disabling it, this still happens.
It's kind of understandable, since the profile database (and received files) are in the program directory. And that's not where they belong. They belong in the user profile directory. If they were located there, everything would work without an error.
So how do we fix this?
For the record, the error I'm getting is:
Miranda was unable to open 'username.dat'
It's inaccessible or used by other applications or Miranda instances
Run as Administrator -> works fine. But as stated, this shouldn't be neccesary. It's bad practice to put user stuff in the program directory anyway, so this needs fixing and not workarounding. Just to be clear.
My system is a Windows 7 x64 SP1, running as a non-administrator with UAC enabled.