Add/Remove Error. Please help!

[WiZZiX]

We recently installed service pack 1 for InstallShield Professional 7. Right now we have to create a new release of our application. This will be the first release after the servicepack 1 upgrade. We encounter the following problems. After (succesfully) applaying a differential build to a working installation, when we try to use Add/Remove programs to modify/reinstall/remove we receive the following three errors.

1 -> Internal error
Error 0x80070057
Description:

After pressing ok:

2 -> Internal error
Error 0x80070057
Description:

then followed by

3 --> Setup "Productname"
The installed version of the application could not be determined. Setup will now exit.

Alle messages are in Dutch. Our installation uses Dutch language.
It does NOT happen when applying a full build, only with differential build.
The initial install script was created using Prof 7.00
Update UI is enabled.
We do not use a modified OnSetUpdateMode, OnMoveData or OnShowUI.

I've been working on this issue for over 6 hours now. I can't figure it out. Please help !!!

Thanks in advance.

Kind regards,

WiZZiX
Joeri van der Well
The Netherlands