"Could not load file or assembly" error when trying to call an external assembly, although it is in GAC and in the project package

Question

I have been working on an empty SharePoint 2010 project in Visual Studio 2010 and everything works as it should until I try to call a certain external assembly - adding a reference to the assembly alone (in solution explorer) is not problematic, but trying to use the assembly in code causes

"Error: Could not load file or assembly ', Version=1.0.0.0, Culture=neutral, PublicKeyToken=...' or one of its dependencies. The system cannot find the file specified."

I have no idea why. Here's what I know:

• assembly with the same name, version, culture and public key token is installed in GAC;
• I have included the assembly in the project package (Package.package - advanced - Add assembly).
• It makes no difference whether or not I specify (in package) 'safe controls' - right now, I have 'Safe' checked, Namespace set to assembly namespace, type = *, Assembly name = empty, 'Safe against script' unchecked.
• The assembly platform target is 'Any CPU', .NET 3.5 - same as the SharePoint project.
• If I create a normal C# console app ('Any CPU' target), I can reference and use the same assembly normally - no error occurs.

Anybody ever had a problem like this?

Answer 1

Somehow, after struggling for days with this, I managed to solve it minutes after posting it here ...

What I did to resolve this was to right-click the project in Solution Explorer -> WSPBuilder -> Uninstall, then Build WSP & Deploy again. Seems there was an old .wsp file that was not getting replaced by simply right-clicking project -> Deploy.