RAM was suggested as an issue here ... it doesnt surprise me that it was this particular server that gave us this problem.
The server is old, and pants, is a DC and only has 1024 RAM. I look fwd to the summer when we becoma an academy with a truck load of cash ... and they can buy me a few goodies! 
A simple restart didnt cure the problem, but power off and on did the trick, again suggesting RAM is an issue.
As for the scheduled reboot ... i used a vbs script:
Code:
' This script will restart the target computer, even if the local screen has been locked
' Create a Scheduled Task to run one time only, and ensure that the reboot time will not affect backups or any other timed services.
strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
& "{impersonationLevel=impersonate,(Shutdown)}!\\" & strComputer & "\root\cimv2")
Set colOperatingSystems = objWMIService.ExecQuery _
("Select * from Win32_OperatingSystem")
For Each objOperatingSystem in colOperatingSystems
ObjOperatingSystem.Win32shutdown 6
Next