Client refuses to update

I have one stubborn server that just refuses to update.

We're using Sep 12.1Ru6

If I reboot the server, bingo , it's updated, but a few days later I'll get an email saying that its out of date, If I clck update policy, nothing, if I push updates to the client (update content) from Sepm, nothing.

There is nothing in the event log, its not a firewall or network issue as a reboot fixes the problem(temporarily)  all my other clients are updating normaly so I can't see  it being the Server.

The Client server is 2008R2 and the Server 2012R2

I'm at a loss, suggestions?