What program are you using when you get this error?
When you purchased the full product, did you do anything to activate Office?
I don't want to be patronizing, but are you sure that the code you entered from the full purchase is correct? Did you mistype any part of it?
Do you still have the disc that you used to install Office with?
If it is correct and you still can't get it activated, does the confirmation e-mail from MS for your purchase provide any way to contact MS? If so, I think that would be your best bet as something is not right there.
Sr. Network Engineer
A+, MCP, MCSE, 15 years of experience