The Windows NTVDM component must be active:

Right click Windows Start Button Flag in lower-left corner of Windows Desktop
Click Control Panel 
View by: Small icons instead of View by: Category 
Click Programs and Features
Click Turn Windows Features on or off
Click Legacy Components
Check NTVDM
Click OK

VetMaster startup settings:

Right click VetMaster startup icon (usually a dog), click properties, Advanced options
  "Run as Administrator" must be NOT be checked 
Options tab
  Quick Edit Mode must be not be checked for Logitech mouse support
  Use legacy console (requires relaunch) must be checked
Layout tab
  Width 80 Height 25 for both Screen buffer size and Window size
  Let system position window must be unchecked

Work stations may randomly disconnect if network cards shut down using power saving.
To correct, get into Device manager http://www.computerhope.com/issues/ch000833.htm 

Click Network adapters, click network card, click Power Management.
Uncheck "Allow the computer to turn off this device to save power".  Do this on all computers.