At our client we're migrating from 2007 to 2010. On top of that the 2010 environment is configured with claims based authentication and Nintex workflow is widely used throughout the farm.
In the testing phase we noticed that running workflows that were running during the migration were crashing. On advice of the Nintex guru (Mike Fitzmaurice) we waited with the switch to claims after the CU of december 2012.
In january we deployed the update on our dev server and migation server and all seemed well. After this step we deployed the CU to all the farms at the client.
After a few days a call was made to inform us that on a library on one of the farms the workflows which should launch on item creation was stuck in starting. First we thought this was due to Nintex because if you look in the sharepoint manager you'll see following custom eventreceivers:
So we logged a case at Nintex but while searching for other persons experiecing this issue I came accros this thread on msdn. I quickly tested if the error also occured with the SPD and OOB workflows and it did. A big difficulty was the ULS logs even on verboseEx didn't any information at all.
Next step was to log a case at microsoft. After some helpfull hints I build a farm with the CU of august and imported the faulty list. The error wasn't reproduced, I installed the december CU and again the error was showing up, in the hope of getting a quick fix with the CU of febrauri 2013 I installed that one too, but no it didn't solve the issue.
Microsoft provided us with some great feedback it was linked with the december 2012 CU. If you have a list/library with required fields. If you set these fields as non required the workflow starts as normal. The only exception here is the "Lines of text" field.
So if you don't need to switch to claims directly you might want to avoid updating to the CU of december 2012 or that one of februari 2013.
Update: the hotfix for this particular issue will be released with the June 2013 CU. But be aware, if you install the hotfix through the CU and apply SP2 of SharePoint these changes will be rolled back, so in order to have the hotfix applied again you'll have to install another CU again.