It sounds like you don't have the most recent version of ArtRage, as we released an update when OS X came out. This is most likely why you are having the problem. Download the latest version from our website by going to the support page here www.artrage.com/ar2support.html then clicking the top question and following the instructions. Artrage 2.5.20 will be installed as 'Artrage 2.5' in your Applications folder by default
If you have any problems, email me the details directly at email@example.com including the text of any error messages, a crash report if available, and details of any problems you had when downloading from the link above if you are unable to. I'll be happy to help, but I'll need this information from you in order to know what the problem is.