The QuickSetup.jnlp provided from http://www.forgerock.org/opendj.html is prevented from being run on OS X.
This appears to be because:
- It is signed by an untrusted self-signed certificate
- The certificate is issued by <cn=OpenDS Test Certificate,o=OpenDS.org>
Using a certificate issued by a "well known" CA to forgerock.org may help.
This seems to be a side-effect of the Gatekeeper functionality in OS X 10.8. If you allow Gatekeeper to run applications downloaded from "Anywhere" (in Security & Privacy preferences) then javaws will let you trust the certificate signing QuickSetup.jnlp and run the program.
You can return Gatekeeper to the default "Mac App Store and identified developers" afterwards. QuickSetup.jnlp can still be downloaded and run.