If you need to change the entered Licencee and/or licence no, got Start > Run
"c:\program files\stock\stock.exe" /configdb:y
which will reprompt you for database type (Jet for free version) and location (the full path to your stock.mdb, for example c:\stoock\stock.mdb), then it will prompt for licencee details.
If the licence details do not appear to be valid, can you send me a PM with the username and password you use for these forums so I can check that the system has indeed sent you valid details. Obviously, don't send these details in a reply here!
Get free EPoS software at http://www.lettronics.com