Add the following line to your Config.sys (or more likely, config.nt) file.
DEVICE=\DOX10.SYS\V24.SYS R2048 S255 Ca Abbbb Icc
Ca is the COM port number C1,C2,C3 or C4
Abbbb if COM3 put A03E8 if COM4 put A02E8 else put nothing
Icc if COM3 put I04 if COM4 put I03 else put nothing
USB to Serial converters will work with DOX10. RSLinx, if it is running, might grab your COM port and DOX10 won't be able to access it, so turn off RSLinx.
Good Luck