For the past few weeks I have been frustrated as all hell with the Ambiguous Reference error appearing in my .NET web application project. I had uninstalled, reinstalled, cleared caches etc, yet nothing worked. This project I am working on is a DotNetNuke module with multiple projects within the solution. I was developing it outside of Dotnetnuke with the web project setup with a Virtual Directory with the dll's built and put into the bin folder of DotNetnuke. So to cut a long story short, but changing the dll's build path back to the projects bin folder rather than DNN's bin folder, the ambiguous reference disappeared.
My dilemma now is that to develop I must change the build folder to the projects bin folder so Resharper won't throw "Ambiguous Reference" errors, but to run and debug the project, I have to change the build to output into the DNN bin folder.