Close Topaz on all the PC's.
Do a reset on the Master and the problem Client PC.
Re-register the Master Topaz, leave the Client Topaz as is.
Read SSL: "How do I re-register Topaz".
Print the registration form, sign it and fax it to Datatex.
If reset serial does not work,
Read SSL: "Reset serial does not change serial number."
ALSO SEE: "Client TOPAZ error with serial after registeration."