Do you have a map service using the SDE database?
I can not re-register the feature class as versioned, any thoughts?
I think a reboot of the server may be the best thing to try? I would probably export / backup any data that I didn't want to lose from recent edits.
How many people have access to the specific DB?
Also, you stated in your initial post that
I assume that you meant the feature dataset, right?