[BlueOnyx:09442] phpmyadmin 3.1.3 problem

[Wisja.net]

I have a 5106R box with phpmyadmin 3.1.3 (purchaced on solarspeed.net last year).
This box isn't used much so I don't realy know when things went wrong, but they are 
now..
There are about 10 sites on this box and few of them use MySQL. I can't get phpmyadmin 
to work through the AdminGUI (gives a page not found error). Also 
http://www.sitename.com/phpmyadmin doesn't work, it gives a HTTP 500 error. 
http://myserverip/phpmyadmin does work fine, so its not something with phpmyadmin 
itself (?)(I also tried reinstalling).

Anyone with ideas?

I have set the MySQL password and in the GUI it says: MySQL connection possible with 
this settings. So I dont believe this to be the same problem that i've seen comming by 
this list before. Or could it be that I have to do the password setting before 
installing the 3.1.3 version from solarspeed?

With kind regards,

Wisja