Did you do a state backup or server backup prior to installing the new version?   Ideally in this case, if you find that an upgrade broke something, you would plan to restore back to a previous version by restoring your servers back to the older version. 

At least that's an option in a virtual environment.

If you create a new workflow using the same context variable, do you get the same result? Create a one action workflow with Log to the History List. Add the reference there and run the workflow manually on an item. Did it publish fine? What was the outcome in the history of the workflow?

Thanks for your replies.

- Backup: the Problem is the database on an other SQL Server.

  We decided not to get back to the old Version and opened a ticket with Nintex. (this is now at the developer. It belongs to the Project update.)

- We can use this variables in normal Workflows. In Connection with the Project part, we get the same error with new Actions .

Thanks

Dagmar

This issue has been identified as a defect (in build Nintex Workflow 2013 for Project Server 3.0.4.0) and added to the list of things to be addressed in a future release of Nintex Workflow for Project Server 2013.