Problem to install cab-files with my HTC Touch HD

Hello all, best wishes for all of you.
I am new on this forum and read many stuff here allready. However i didn't find a real solution yet for my problem to get cab-files installed, f.e.:

I'd like to install Gyrator 2 on my HTC Touch HD (UK)
When i try this i get this error:

The file "gyrator" cannot be opened. Either it is not signed with a trusted certificate, or one of its components cannot be found. If the problem persists, try reinstalling or restoring the file.

The same message occures when i try to do this with other cab-files. GSen was going fine and even CabInstaller did. Net Compact Framework 3.5. installed and ROM version: 1.14.401.3

I copied the cab-files from PC to PPC by dragging it into the Storage Card.
I would really appreciate your help!

Tia ....