1999 Convertible won't open roof all the way?

[obersturm]

Hi all,

A friend of mine bought himself a 996 4 Convertible recently. Just before the deal was done the roof started playing up and it stops when it is up 90 degrees in the air and won't budge going down all the way.
It closes and reopens to that point no problems?
We checked handbrake and engine lid switches as well as disconnecting the battery over night. Didn't help.
Is this a common problem?
Did someone had this before and how was it fixed?
Does it need to be connected to a system tester to "relearn" its
Limit switches or something?

Any help would be highly appreciated.

Thanks and best regards

Marty