Unable to publish workflows after update rollups

I just encountered an interesting problem today where I was unable to publish a workflow - the friendly error message said "An error occurred when the workflow was being created. Try saving the workflow again". I found a handy discussion here: http://social.microsoft.com/forums/en-US/crm/thread/78a7f940-50de-4f83-a38d-54425dd0ec1c/ that explains the solution. This seems to have started with Update Rollup 2 (and in this case I just applied UR 3 last week) and just requires adding an assembly line to the web.config in the section :



I didn't even need to reset IIS and the workflows started publishing again.