I only know of a few reasons why this might happen:
1) You changed your PC's system clock after exiting the Tournament Director software the first time. This can sometimes trigger a premature end to the evaluation period. Unfortunately, this cannot be reversed. Only a valid license key will unlock the software at this point.
2) You are not logged in as a user with Administrator privileges. If so, try logging in (to Windows) as a user with Administrator privileges and re-running the software. Also, if you are running Windows Vista, you can try right-clicking on the Tournament Director shortcut and selecting "Run as administrator".
3) You have anti-virus or anti-spyware software (or perhaps some other software) running that is preventing the Tournament Director software from accessing the Windows registry. The software stores the license in the registry, and if it cannot be accessed, it defaults to unlicensed mode with the evaluation period expired. Restoring access to the registry should fix the problem.