Demand Management Workflows fail to start after Nintex upgrade.

Issue

After upgrading Nintex Workflow and Nintex Workflow for Project Server, Demand Management Workflows might fail to start and the following error might appear when clicking on a project:

Error Code

Unable to open the project. The project has not been properly initialized. This may be caused by the workflow associated with the Enterprise Project Type not starting correctly. Please contact your system administrator

Resolution

1. Restart "Project Server Application Service" on all WFE servers by going to Central Admin -> System Settings -> Services on Server -> Stop
2. Start the "Project Server Application Service"
3. Restart "Microsoft Project Server Queue Service 2013" from Windows Services.