From the ArchiCADwiki:

Breaking news – Disabled Java plugin on Mac

Update 02/01/2013: Apple has recently blacklisted the Java Web plugin, as a result GRAPHISOFT’s key plug programming site (https://upgrade.graphisoft.com/) is not working on Mac systems. In some cases the site returns Java is outdated message, in other cases it just displays the standard error message, linking this site.

With the latest OS X updates Apple has added a security mechanism that forces Safari to use a minimum specified version of the Java plugin. At any given time Apple can remotely change this value on all online Apple systems. This was the second time this month that they set a value that references a Java version that is not yet available, to quickly respond to Java plugin based vulnerabilities.

Read the full ArchiCADwiki article here

If you run into this issue and the full ArchiCADwiki article doesn’t have your answers, contact your local ArchiCAD Reseller for assistance. They’ll know what to do. Or you know, shoot me an e-mail. I can help too.

OR….

Just install the latest JAVA 7 Update 13 which was released today. Thanks Karl for pointing this out. Hopefully this is a long term fix.