TGS uses a temporary file (a work file) when stations access the point of sale. This file can become corrupted by having an active screen saver, power management activated, duplicate station numbers in TGS or by using Ctrl/Alt/Del to terminate the software while you are in point of sale.
Reboot the computer.
If the problem is still present, reboot all systems on your network, and before using TGS again, navigate to the \TGSData folder and delete all of the following files: POSWRKxx.tmp (where xx is a number 01, 02, etc.). You may need to stop the Pervasive Database service before deleting the files.
Open The General Store on each workstation.
Check the bar at the top of the screen. Each station number should be unique. You should "force" each station to log in as it's unique number. For instructions click here.
On each workstation, disable any screen saver and set Power Management (in Control Panel) to "None"