OAB get prompting password

If you have enabled web-based publishing of your Offline Address Book (OAB) and your Outlook users get continuously prompted to enter their passwords, you need to check a couple of things:

Make sure Autodiscover is working perfectly before you made the OAB change.
Hold down the CTRL button and right click on the Outlook icon on the task bar, then select Test Email Autoconfiguration. Unselect GuessSmart and Secure GuessSmart and keep Use Autodiscover selected. On the Log tab, make sure Autodiscover is successful and that it was able to bind to an SCP.
Make sure that the autodiscover.domain.com entry is added to your certificate’s Subject Alernative Names list.
If you are facing problems with Autodiscover, you should correct that first before attempting the steps mentioned below.
Make sure that you have defined the External and Internal URLs for the OAB virtual directory in your client access server.

Once you have made sure that Autodiscover is working OK, and that the credentials are being prompted for the OAB URL (and not the mailbox server), you need to check the IIS Authentication setting on the client access server.

On the Client Access Server running Windows Server 2008, open IIS Manager console.
Click on Default Web Site
Open Authentication
Note that only Anonymous Authentication is enabled. All other authentication methods should be disabled.
Temporarily enable Windows Authentication
Right click on Windows Authentication and choose Advanced Settings
Uncheck Enable Kernel Mode Authentication and click OK
Disable Windows Authentication
Do an IISRESET