I have been working on a MOSS deliverable for a new client. I configured my Debug properties of the project to point to the target web application, but when I press F5, I get the following message: This solution contains two assemblies with the same name, or the SharePoint server already has an assembly with the specified name After a bit of investigation, I found the culprit - I had added a post build event to push the dll into the GAC. "C:\Program Files\Microsoft SDKs\Windows\v6.0A\Bin\gacutil.exe" -i "$(TargetPath)" This meant that Visual Studio 2008 was finding an assembly in the GAC when it was not expecting to find one. The resolution was: 1. Remove the dll from the GAC 2. Remove the post build event I could then rerun the deployment and continue fixing my code ....