This message is usually displayed when you attempt to open a paid version of Unity without having a valid license. If you've recently switched to a new computer and you're attempting to open a paid version of Unity, you will need to transfer your license from your old computer to your new one.
You may also need to log in to your Unity account to activate your license on the new computer. If you're still having trouble accessing your Unity projects, you can try contacting Unity support for further assistance.
