Cannot Export Crystal Reports .NET version 13

I have an asp.net 4.0 application running with CR.NET version 13.

When i host it on a w2k3 R2 server running IIS 6 when trying to export the report to pdf on the report viewer i got this error (it tried to download to the browser but then i saw this message popping up):

"Adobe Reader could not open 'xxx.pdf' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded)"

When I tried to export to Excel or Word format I got a blank document opened.

I have no such error and problem when hosting it on w2k8 server running IIS 7.