Inheriting a new SharePoint environment is so fun (not) because I get to come across wacky errors like this. Luckily it only gave me bad dreams for a couple of days.
The workflow failed to start due to an internal error.
Trobleshooting Steps Taken:
1. Reproduced using a fresh Document Library in the same site.
2. Reproduced on another site in the same Site Collection.
3. Did not reproduce in a different Site Collection in Farm.
4. Performed a STSADM Export/Import to a dev farm: could not reproduce error.
5. Looked at diagnostic logs, Event Viewer: Not much going on there.
Solution:
Now if you go out and do some googling, there’s quite a bit of chatter about this error with all kinds reported solutions ranging from uninstalling/reinstalling the workflow features to modifying feature XML files and all kinds of other stuff. The one that got me to a resolution was this one.
But wait, there’s more!
I thought since the approval workflow that I was working with was the suspect one that deactivating/reactivating the feature for the “ReviewWorkflows” feature would fix the issue. It didn’t. What I had to do was deactivate/reactivate all of the workflows like so:
stsadm -o Deactivatefeature -name TranslationWorkflow -url http://SiteCollectionURL stsadm -o Deactivatefeature -name ReviewWorkflows -url http://SiteCollectionURL stsadm -o Deactivatefeature -name SignaturesWorkflow -url http://SiteCollectionURL stsadm -o Deactivatefeature -name ExpirationWorkflow -url http://SiteCollectionURL stsadm -o Deactivatefeature -name IssueTrackingWorkflow -url http://SiteCollectionURL stsadm -o Activatefeature -name TranslationWorkflow -url http://SiteCollectionURL stsadm -o Activatefeature -name ReviewWorkflows -url http://SiteCollectionURL stsadm -o Activatefeature -name SignaturesWorkflow -url http://SiteCollectionURL stsadm -o Activatefeature -name ExpirationWorkflow -url http://SiteCollectionURL stsadm -o Activatefeature -name IssueTrackingWorkflow -url http://SiteCollectionURL
So after deactivating/reactivating all the workflow features listed above, the Site Collection was happy once again. 
