Had the same problem with DW8. I was in Texas and the disc was in Toronto
I tried "Control Panel>Add/Remove" click the program and click the change button then choose "Repair" from the Dialog box, did'nt work for me but worth a try. My solution was to uninstall, then download & install the "trial" from Macromedia's site. I guess the uninstall leaves the serial info in the "Registry" or something, not sure but everything is working just fine. Hope this helps and good luck.