If you run into the situation where Outlook keeps prompting you for credentials when you have a Deltek Collaboration feed into Outlook, you will need to remove the calendar and re-add it to stop the prompting. To remove the Deltek Collaboration calendar feed, in Outlook 2010/2013, go to File > Account Settings > Account Settings > Published Calendars. Delete the Deltek Collaboration calendar from this section. Deleting the calendar will stop the Outlook prompting. If you wish to put your Deltek Collaboration calendar back into Outlook, you can re-establish the connection.