"An unhandled exception occurred in the user interface": Error message when you try to start the Search service in SharePoint 2007

This behavior occurs if you do not use the "domain_name\user_name" format when enter an account name in the User name field. This field is next to Farm Search Service Account on the Configure Office SharePoint Server Search Service Settings on serverServerName page.

To work around this behavior, use the ""domain_name\user_name" format when you enter an account name in the User name field.

Please refer http://support.microsoft.com/kb/928620 for more details.

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