Cant perform Guest Windows Update

Hi there.

I am having problems on a ESXi 5.1 host running Windows 2008 R2 guest O/S in that the windows update fails with the error message

"An error occurred while checking for new updates for you computer"

with error code

Code 80072EFE

Googling this hasn't come up with much useful. I have a guest with VMware tools installed and another without. Same problem on both. The host running ESXi is part of a vcentre 5.1 cluster.

What is the obvious gotcha that i have missed :-)

Thanks