Scenario: When scheduling a meeting, adding the conference room, etc., everything is fine until you add above user as a required attendee. When the user is added, the conference room disappears from the scheduling assistant. Causes for Conference Room Disappear: As per MS article, the issue could be due to following reasons. User mailbox may contain an '&' symbol in the SMTP email address which Outlook 2010 dont like (this is not the case, SMTP address was fine)white space characters and decimal point characters at the end of the mailNickname (AD)attribute (this is not the case, no additional characters)User Calendar Working hours misconfiguration, (The end time entered occurs before the start time) This caused issue and accessing user calendar thru OWA gave following error How it is Resolved? Changed users working hours from 4:00PM to 1:00 AM (This was causing the issue) To Standard Default working hours 8:00 AM to 5:00 PM This change resolved issue.

This Is RESOLVED