Misbehaving Appointments locking up GW

GW 2014 client 2014.1
To my knowledge only 1 user

User receives an appointment request and opens it. The Appointment window opens and then its display starts to jump around (only way to describe it). The lower portion of the window's cursor moves up and down on its own; the display jumps from the top to the bottom highlighting different areas, etc. And it and the main GW window are frozen and the only option available is to right click on the task bar and close all GW windows.

The user can then re-open GW and right click on the appointment and accept or decline but if it's opened again the same thing happens.

I completely uninstalled GW and reinstalled, and even updated the video driver. Cleaned up all the temp files on the users PC and none of that has changed the behavior.

Short of reverting back to the 2012 client I am not sure what to try next.

Any ideas are welcome.
- psp