Patches with Wise

I use "Wise for Windows Installer 5.0 Enterprise" and want to make a Patch for my program. I do like written in the readme, but when I give the patch to others to install it they always get an error such as "Not a correct package file. Please contact the distributor for help.". I don't know the exact english text because I'm german (and my package too ;)).
Any Idea how to create a patch for a Wise Installation?