Problem symptom:

Working with mixed environment of Exchange 2003 and Exchange 2010.

Migrating and new creating Room mailboxes on/to Exchange 2010.

When user send meeting invitation that room is invited in it, the room is not auto accept as configured.

Problem cause:

Form mismatch.

– could be developed form that implement to organization that is not working well with Exchange 2010.

Solution:

1. Fix the form that it fit the requirements of Exchange 2010 form base.

2. Interim fix: disable using form on Outlook client when sending meeting with auto accept needs (see attach screen shot).

==========================================================================================

Fault form could also cause OWA accept/decline/tentative response error (see OWA screen shot).
Additional details:
Error
—-
HTTP error. The server cannot fulfill the request.
Details
—-
Mail could not be sent.
==============================================================
Request
Url: https://server.company.com:443/owa/ev.owa?oeh=1&ns=EditMeetingInvite&ev=EditResponseInvite
User host address: xxx.xxx.xxx.xxx
User: User Alias
EX Address: /o=Domain/ou=Exchange Administrative Group/cn=Recipients/cn=User name
SMTP Address: {user name}@company.com
OWA version: 14.1.255.0
Mailbox server: {Server name}.company.com

Exception
Exception type: Microsoft.Exchange.Clients.Owa.Core.OwaInvalidOperationException
Exception message: meetingRequest.UpdateCalendarItem returns null.

Call stack
Microsoft.Exchange.Clients.Owa.Core.MeetingUtilities.UpdateCalendarItem(MeetingRequest meetingRequest)
Microsoft.Exchange.Clients.Owa.Premium.EditMeetingInviteEventHandler.EditResponseInvite()