Bought the disc at staples; I had trouble transferring last year's info so switched to on-line version and completed my return. I have the serial number but can't use it?

Unfortunately, a CD/download purchase is not transferable to the online edition.

If you decide to stick with the online version, here's how to get a refund on the CD/download edition: https://turbotax.community.intuit.ca/replies/2647900