**The CD version as well as the download version as of May 18, 10am EST, 2011 does not contain this bug.**
There has been a last minute SNAFU with the Mac download version of CM:BN, which limits the entry of the license key to 19 digits (instead of 25). The download version has been replaced already and is working correctly now, so you can simple re-download that.
Alternatively, grab the Hotfix from www.battlefront.com/patches. Make sure to follow the installation instructions contained in: http://www.battlefront.com/community/showthread.php?t=96803