The Com port that the thermal printer is connected to must have "Flow Control" set to "Xon/Xoff".  This can be accomplished by doing the following:

Windows XP: 
1.) Click Start and select "Printers and faxes"
2.) Right click the Thermal Printer and select "properties"
3.) Select the "ports" tab
4.) Select "Configure Port"
5.) Select "Xon/Xoff" from the "Flow Control" drop down menu.
6.) Click "OK"
7.) Click "OK"

Windows 2000: 
1.) Click Start then select "Settings" and then "Printers"
2.) Right click the Thermal Printer and select "properties"
3.) Select the "ports" tab
4.) Select "Configure Port"
5.) Select "Xon/Xoff" from the "Flow Control" drop down menu.
6.) Click "OK"
7.) Click "OK"