Getting "failed to start" with a SharePoint workflow

I have been playing around with some workflow code for a demo I am doing. This has meant creating and deleting a workflow project as I refine the demo. Whilst going through the process of a delete and recreate of the workflow (using the same name for the project/workflow but creating a new project from the VS file menu) I hit the problem that when the new version of the workflow was run I got a “failed to start” error.

After checking the SharePoint log in the 12 hive I found that workflow runtime was trying to load the code beside assembly using the old assembly name name/public key, which obviously it could not fine as the new version was in the GAC. Once I correct and redeployed the workflow.xml file (with the old PublicKeyToken for the CodeBesideAssembly) all was OK