If Outlook 2010 constantly asks for logon information in an Exchange 2010 environment, the following procedure can help. If you have not already done so, you should first install the latest service pack and update rollup for Exchange 2007. Which rollup is current can be found here.
If Outlook still asks for login information after installing the updates for Exchange 2007, it may help to uncheck the "Use kernel mode authentication" box. To do this, open the IIS Manager and click on "Authentication" under "Default Web Site".
In the advanced settings for "Windows authentication" you will find the "Use kernel mode authentication" checkbox. This can be removed, if this procedure does not help, the checkmark should definitely be set again.
Another possible reason for requesting login information may be saved login information on the client. This logon information can be deleted under Control Panel -> Logon Information Management on the client.
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