Since i don't have any more details despite custom errors off and debug on, i don't have much more to say. Here are some points of interest:
- Regular ASP.NET MVC /controller/action URLs work on iis 6
- I've added wildcard isapi filter to iis 6 although i think it is not needed in .net 4
- WebAPIs work on local IISExpress server so it shouldn't be a serialization error
Does anyone have any idea what could be the problem? If not, at least it would be nice to find a way to have more detailed error messages.