When clicking Save or Publish on a workflow you may get an error message that reads:
soap:ServerServer was unable to process request ---> The ConnectionString property has not been initialized.
The reason for this error, or one of them anyway, is that there is no Nintex Content Database defined for the site. I create my sites with PowerShell and very rarely will the script complete but no DB will be created. So when I got a message from my developer that there was an issue I was perplexed. The solution for this is to simply go and create the DB in Central Administration and associate the site.
If you (or if you are an administrator and one of your workflow developers is doing all this) you may get the following error reported instead of the one above:
This will happen if you attempt to republish after the initial error. The reason is that a directory is created with your workflow name as the title at <your site url>/NintexWorkflows and it will be empty. To resolve this simply go to that URL and delete the directory. There should be no files underneath since a DB was never created for the site. Having removed this directory and created your Nintex Content DB association you should now be able to save and/or publish your workflow.