I've found that if I have CX-Programmer (PLC programming software from Omron) running, the ESC key completely stops working. I've only found one other reference to this conflict which can be seen at this link, but it is in AutoCAD LT.
http://forums.autodesk.com/t5/AutoCAD-LT/AutoCad-2012LT-problem-with-Esc-button/td-p/3638462
By accident, I discovered that the "gman.exe" process within CX-Programmer will cause the conflict by itself (it wasn't terminated correctly when I closed CX-Programmer). Other processes may cause the problem also, but in this case as soon as I ended "gman.exe" from task manager the ESC key began functioning correctly.
I'm running CX-Programmer v9.31. I've reported this to my Omron distributor and will post any helpfull info that comes from their side. I'm curious if anyone else is experiencing this issue? Any solutions or work-arounds?