It would be interesting to see, what your LOG reports if a file cannot be downloaded because it is an unknown MIME type.

Would it be possible for you to check this? Create a simple empty SetupBuilder project and use the "Download File..." script action to download a file with an unknown MIME type (so it gets blocked). Do you see such a download request in your LOG? What does "Download File..." stores in %_SB_ERRORCODE% after such an unsuccessful action?

I know it does not help at all to solve your problem, but I am 100% sure it is not caused by SetupBuilder (otherwise we would have seen thousands of support requests since the last recompile of the HTTP component in May 2014).

Friedrich