I'm having trouble replicating the conditions for this, but I have frequent trouble on my site adding responses to dialogues. Often I receive: Insert Entries: Could not insert dialogue record!
Two things that strike me. I began having trouble when we began to cache. I began having trouble after a couple teachers had dialogues with 90+ entries.
I'll keep looking for specifics that trigger the error. My site has no custom elements and is on a fresh CVS.