Do you have any of the MSPs installed?
Does the machine have a current inventory scan?
Is this only one scheduled task or numerous tasks?
Do you have any firewalls turned on?
Delivery Method for the task what is Type and Frequency?
Client OS is it windows Vista/7 with UAC on?
On the core is the LANDesk Scheduler Service Running - Try restarting.
Sometimes a Scheduled task becomes corrupted and I have had to recreate it from scratch but that is rare.
Usually running this on the Client and then rebooting the machine fixes this issue for me:
net stop "LANDesk Policy Invoker"
"C:\Program Files (x86)\LANDesk\LDClient\clientdbutil.exe" /create
"C:\Program Files (x86)\LANDesk\LDClient\clientdbutil.exe" /validate
net start "LANDesk Policy Invoker"