Hi again!
We are sorry you are going through this, but in our experience VS setup projects have quite a lot of quirks. Our Cassini itself is not much of a trouble, but getting to know VS Setup can be unpleasant in the beginning.
It seems you may have another instance of UltiDevCassiniServerConfiguration.dll inadvertently included in the setup project. Please see if you have two of those and remove one that does NOT point to the correct installation location. Then re-add custom actions again. If you are positive that you have only one instance of UltiDevCassiniServerConfiguration.dll, please consider creating a test setup project from scratch - something seems off with the project as custom actions engine thinks UltiDevCassiniServerConfiguration.dll is installed into sub-folder of System32.
Regards,
UltiDev Team.
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