Dual screen issues

[gmagbee1]

I have a problem with my 17" apple monitor. The right side of the screen has a 1" black stripe running top to bottom.

My set up:
I have a Dual 1.25 G4 with 1.75 ram
It has a 22? Apple display and a 17? Apple display
I am using a Gefen Extendit on the 17? screen
I am using a 9800 pro mac edition card

I cant get rid of the black stripe. I tried the display changes in my system preferences.
I can't adust the resolution on the 17" but can on the 22".
The 17" acts as though it is not set at the full resolution.
I purchase the card first. Then The extend it.
Before the changes both monitors worked well together
I would appreciate any help