While checking the logs at work I found this curious error “Invalid_Viewstate_Client_Disconnected”. After some research (i.e. Google) I found this knowledge base article Intermittent Invalid Viewstate Error in ASP.NET Web pages. Unfortunately, the KB didn’t help much since we were doing all of the recommended steps. I did find this post which defined the problem as the user canceling the postback while the viewstate was being sent to the server. This issue tends to occur when the viewstate becomes very large. I found another post that pointed the blame at a proxy server truncating the viewstate if it was over 2K. Both posts suggested having a smaller viewstate or ignoring the error. Our users haven’t complained about the error and we haven’t been able to reproduce it so I’m ignoring it for now. But if this becomes a problem I’ll post our solution here.