BUE2012 - "Unable to establish trust", "Invalid parameters for interface"

Hi, just installed BUE2012 with SP1a on a clean install of Windows Server 2008 R2 SP1. Everything appears to work OK but when I was receiving GRT

errors on one Hyper V server when backing him up via the Hyper V Agent even though the Windows Agent is also installed on all VM's.

So, I have gone to the Servers view and clicked on them to try and establish the trust again but get the following error on all VM's I try to do this with:

Anyone else seen this and know a fix?

Thanks.