Last week I setup a second primary server for redundancy. Everything seemed to work well so I left it alone for several days so everything could sync up. I started getting calls that Vista / 7 logins were very slow, users would press CTRL-ALT-DEL to login and get a blank screen for a few mins before logging in. Once logged in life was good. I checked DNS and everything looked OK both ways. I removed Zen from that server and had a lab of 40 machines refresh then reboot. The problem was gone. Any thoughts on what could cause this?

It's Zen 10.3.3 on a 2008R2 server (both were)
MSSQL 2005 Enterprise for the DB

Thanks for any input!