Error after replacing home directory

[FishermensFriend]

Hello, I have an iis 5 at work with .asp files and some .dlls, same thing with the customer. When I try to "update" the customer's home directory with a new version (delivered packed from my local directory), i get a white screen or 404 errors. when i just replace single files it works, but replacing a complete directory always fails.

There are no frontpage server extensions configured on both servers.

Of course I reset the IIS after replacing the files.

Any ideas? I would appreciate every suggestion.

Thank you!