Which mac OS version are you using? If you'er using OS9 or earlier, update to the most recent java update: MRJ 2.2.6 for OS 9.2.2 http://docs.info.apple.com/article.html?artnum=120209 OR MRJ 2.2.5 for OS 8.1-9.2 http://docs.info.apple.com/article.html?artnum=75097 & also Rebuild your desktop after installing any new softw; ie: hold down CMD+Option keys whilst restarting.

For OSX see: SAFE Restart & Repair Permissions & if necessary see: these suggestions for repair & installation.

Post back to tell us how you go.