I ran the 'check for update option' on the 1.5 Pro I purchased earlier this year and installed 1.6 Pro. When I ran it it asked for a key. I used the one most recently sent to me and it said it was invalid. Luckily I still had a copy of the 1.5 installer, so I was able to get going again.
Should it work like this?
Updating from 1.5 Pro to 1.6 Pro invalidates key
Actually yes and no. Old keys from 1.5 and earlier versions of EZOS will not work with the new 1.6 version. However, all currently registered users get this update for free. Therefore, please email us (ezsupport[at]ezoutlooksync.com) your registration name and hadrdware id and we'll issue a new key for 1.6 version to you. Thanks and sorry for possible inconveniences.