Could not load type from assembly error

If you have one project referencing another project (such as a 'Windows Application' type referencing a 'Class Library') and both have the same Assembly name, you'll get this error. You can either strongly name the referenced project or (even better) rename the assembly of the referencing project (under the 'Application' tab of project properties in VS).

Is the assembly in the Global Assembly Cache (GAC) or any place the might be overriding the assembly that you think is being loaded? This is usually the result of an incorrect assembly being loaded, for me it means I usually have something in the GAC overriding the version I have in bin/Debug.

The solution to this for me was not mentioned above, so I thought I would add my answer to the long tail...

I ended up having an old reference to a class (an HttpHandler) in web.config that was no longer being used (and was no longer a valid reference). For some reason it was ignored while running in Studio (or maybe I have that class still accessible within my dev setup?) and so I only got this error once I tried deploying to IIS. I searched on the assembly name in web.config, removed the unused handler reference, then this error went away and everything works great. Hope this helps someone else.