Hello Mario,
I'm not sure why you are encountering this. In order to get more details about what happens can you download the following
debug DLL, replace the original one from the install folder of Advanced Installer 12.5.1 (e.g. C:\Program Files (x86)\Caphyon\Advanced Installer 12.5.1\custact\x86) on your machine and rebuild the package?
Just replace the original iis.dll from the install folder of Advanced Installer with this one, then restart the application and rebuild the package. This DLL should create a debug log (at install time) on the root of the OS partition (e.g. C:\AI_IIS.log), which can give us more details about the problem. So, can you send us the AI_IIS.log file, to
support at advancedinstaller dot com, after you will build and test your installation package using the debug iis.dll?
Also, you should back up first the existing iis.dll.
Best regards,
Dan