WSPBuilder cannot find my assembly

Question

I am using WSPBuilder on Visual Studio 2010 to create a feature with a feature receiver assembly for SharePoint 2010. When I try to build the WSP using WSP Builder I get this message in the output window:

The assembly MyAssembly.dll is unmanaged. The assembly will be excluded from the WSP package!
The defined Project Assembly seems not to be a valid assembly!
Solution compatibility: SharePoint 2010

The resulting WSP that gets built does not contain my DLL.

My DLL is strongly named, and I cant think of any other obvious reasons why this is happening. Any idea why WSPBuilder is not able to package my assembly in the WSP?

Answer 1

Ahh... Found the answer. My code was getting compiled against .Net Framework 4.0. Changed it to .Net Framework 3.5 and Voila! WSP gets built without any problems...