Are there firewalls enabled on the clients? If so have you made exceptions for communication between the endpoints and LANDesk Core server?
Edit: Forgot to mention Patch Manager should have a "Patch" that can configure windows firewalls to allow communication to the LANDesk core. I believe the current version is LD-ICF-CONFIGv3; but would want confirmation from someone with more experience knowledge.
This patch should be available in your patch location if you have already downloaded patch content. filename is ICFConfig-v7-w7.exe for Vista and Later client OS and Server 2008 and later Server OS.
ICFConfig-v7.exe for XP and Server 2003.
HTH