User not logging into zcm on server logon

when we put the 11.2.3.a agent on a windows 2008 R2 server and login to it the user does not automatically login into the zone as it does if the agent is on a windows 7 box ?

i can right click the zen icon in the system tray and select login andthat works fine but why isnt it logging in to the zone when i log intro the server ?

Cheers in advance

Gareth