When I open Capture One, I receive the error message "Capture One seems to have expired" and the software is not launched.
The first thing to do is to make sure you are not using an early beta version which had an expiration date. You can download the latest version of Capture One here.
If you are working with a current version, this problem is related to the Time and Date settings on your computer. The Date needs to be set to the current date. To do this, open System Preferences and choose Date & Time. Then tick the checkbox "Set date & time automatically".