Exchange 2010 with outlook 2010 authentication pop up

hi every one,

We have a basic exchange 2010 hub/mail/cas on one box. What happens is the following and i can't pinpoint where it could be.

When i start outlook 2010 it will come up with an authentication box.

Now I trobleshoot this as follows:

I start outlook.exe /rpcdiag :

It will try and connect to the addressbook (TCP/IP)

Then the e-mail and then it will stop and give an authentication box

I fill out my credentials and i am connected but then connected throug a proxy it says and ssl

however if i jus say connect again, it will connect fine through tcp/ip. Furthermore it seems to particularly happen when u log off and on aagain and then start outlook 2010 and then again..not always

so i can get to my autodiscover url without probs from the client no pop up

Any one has an idea? is it some sort of latency ?