This looks like something related to powerpack of course, but are you sure you are not logged in as a user restricted to a folder that has been deleted? It would look like that based on the error message ...
I think this have something to do with your hosting configuration.
I seen this one time before (the hosting stats script was enabled).
The thing is that when you send login data to the php file, it includes an extra text at the end (that was an hosting stats script) and it can't be recognised by the php.
I'm not really familiar with this kind of stuff. So, you may ask your hosting provider if there's anything like this...