Outlook Anywhere asking for password

I've tried to set up outlook anywhere using Exchange 2010 and it works well except when Outlook is first opened, the user is asked to enter their windows login password. Once it has been entered everything is fine but I need to get rid of this annoyance.

I've tested the settings on www.testexchangeconnectivity.com and everything is reported as ok. Does anyone know how I can fix this?

I managed to get this working by using NTLM authentication.

In the EMC I enabled this by going to Server Configuration ? Client Access and the properties of the mail server. Then on the outlook anywhere tab chose NTLM authentication as the method.

Then on outlook, in the account settings > more settings window > security tab I set Logon Network Security to NTLM and in the Connection tab > Exchange Proxy Settings chose NTLM authentication

And then it worked!