I received an 'unknown error' bidding or sniping on an item? What happened?

The most common answer is that eBay changed something, and JBidwatcher was unable to recognize the response from eBay. JBidwatcher keeps error pages, until the program is shut down. You can view them (if you haven't shut JBidwatcher down yet) by choosing the auction which had an issue, right-clicking (or control-clicking on a Mac) and selecting 'Advanced', and then 'Show last error' to see what happened.