What patch are you trying to apply?
What version of Mac OS X?
Do you have any options in your Custjob discovery disabled?
If you add a host file entry does it work?
The problem is with both 10.5 and 10.6. The patch I was trying to apply was the lastest firefox 3.6.25 patch. The client is communicating with the core just fine. I ssh'ed in to the machine and I was able to run a vulscan just fine. Also I can run the default inventory script that comes with the product just fine. The problem seems to be with pushing a patch to the client via the core initiated vulscan.
Once the machines were rebooted the problem goes away. I have tested this on about 10 or so mac's. Both 10.5 and 10.6 and they are all exhibiting this behavior.