It has nothing to do with Window 7.
Please check that you are logged with the eBay user id, which was assigned with this key (you can check your Order Confirmation e-mail for that information).

If you are still having problems, you can contact me using Contact form and supply your eBay user id and registration key so I can check.

Have just loaded windows 7 and myibay appears to work OK. However, there does seem to be a small problem, I have cut and pasted the serial number but the 30 day evaluation notice continues to appear. Do you have an answer? Thanks