Watchdogd reports com.apple.WindowServer unresponsive

Topic says it...I have remote admin enabled, so I was able to capture this from the system log. Symptoms when this happens are the keyboard is unresponsive besides the capslock key, and the mouse can move, but you can't press any buttons. This started on 10.9.5, and now I am seeing this on 10.11.1. This is on a 2009 24" iMac. Card is Nvidia....any hints on what to look at?