This error message is displayed if you have upgraded to a new major version or downloaded an upgrade from the Redgate website which reverts to trial mode. If you have a license and you run into this error you will need to activate your serial key within the tool. You can do this one of two ways depending on the product:
On the Help menu, select Manage my license
On the Help menu, select Enter serial number
This will put you back into licensed mode.
If the problem persists you can run SSMS as administrator and then try the activation again.