Glad to be able to help.

I'm working right now but will check things out at my end this evening. I'll watch for a while and see if the problem is still there. One more thing that I didn't mention was that the error seems almost random. It's not always at the end of a round. Sometimes I'll get 10 to 40 rejects in a row all saying unknown work. Then right back to accepted shares.

I wish I was more knowledgeable about this so I could be more help on my end. I think bgminer might come with a logging option. If it does I'll try and record something for you.