When creating a new custom workflow project using Visual Studio 2008, a strong key file (.snk) file is automatically included in the project to sign the workflow assembly. A few days ago, I started developing a SharePoint 2007 Sequential Workflow project. After finishing developing the workflow, I deployed it and started testing it by associating the workflow to a content type (Site Settings > Site Content Type Gallery > Site Content Type > Workflow settings). I then noticed that the strong key file that was being used to sign the workflow assembly wasn’t the one I usually use and modified the project settings so that it started using it. After recompiling the project and redeploying the workflow, I started to get an error message: "New instances of this workflow template are currently disallowed". The reason for this message to appear is that a new version version of the workflow had been deployed (same assembly with a different public key token due to the change in the strong key file used to sign the assembly). In these situations, the existing workflow associations made from older versions of the workflow are automatically set to "No New Instances", meaning that new instances of the workflow for those workflow associations are not allowed. The image below shows the Remove Workflow page with my custom workflow association set to "No New Instances". To access this page, go to Site Settings > Site Content Type Gallery > Site Content Type > Workflow settings > Remove Workflows if the workflow is associated with a content type.
To solve the problem, all you have to do is to set the workflow association to "Allow" and new instances of the workflow can again be created.