Also having same problem....

I was operating fine until I turned on pop3 for users. Even then the problem did not occur.
It started the very first time I called for a pop3 down load.. It has totally disabled me...
All users get a normal display when they log in, but as soon as they click ANY feature they get this error.
I also get it from admin when I click on any users "email"
I have since turned off pop3, reinstalled and still can not get back to a normal operation.

Bill