CAT now has in its default configuration a limitation. You can execute only 500 tests in a single run.
In order to raise the limit to 2500 tests in a single run, you need to register.
Follow a simple procedure described in the link and get a license key. The guide also includes information how to apply the key.
CAT is not yet ready for the market, but it is prepared :) We already can generate a license key and unlock CAT for you using a license key.
For Joyuful Craftsmen people only: you can find a valid license key for CAT in the developers KeePass file. Follow this guide to unlock your CAT instance: How to Apply a License Key.