Problem:

You get the following error when publishing a Nintex workflow:

'soap:Server Server was unable to process request. ---> System accounts can't create a Workspaces.'  

Solution: 

1. Go to the settings of the Collaboration Manager and set the Workspace Creation to 'Workspace created by custom Workflow or web service'.

2. Publish your workflow.

3. Set the settings in the Collaboration Manager to automatically create Workspaces.