Did you try to reinstall the program (or at least to copy the program file and its icon from the installation archive) and entered the reg key after that ?
Are you sure you entered the reg key correctly (with correct case and differentiating between the letter O and the number 0) ? Can you use cut & paste ?
I am not sure if the contact data is coded in the key, too (like with TurboPrint). Did you enter the same name and address as when you registered first ?
Oh and on which platform does this happen ? On WinUAE with a HDD directory registration does not work, you have to use a HDF.
Bye,
Thomas