Your calendar couldn't be checked to see whether this event conflicts with other events.

[Bill Hixon]

We've been using Office 365 for about two years, and we've had a few rooms setup  as resources this entire time.  The Administrative Assistant schedules the rooms and it's worked well for us.  Lately she started getting the notice

"Your calendar couldn't be checked to see whether this event conflicts with other events." 

in emails requesting the rooms.  It's not every time, just often enough to be frustrating.

Any idea why this started?  All the staff making the requests and the rooms are in the same domain and under the same license.  Nothing is on premise.  Everything I could find through searching dealt with on premise exchange servers or google app requests. 

Thanks!

[#2]

Bit late but for others who find this page, I resolved this with the following powershell command:

Set-CalendarProcessing MeetingRoomName -ProcessExternalMeetingMessages $True

[#3]

Mr Mooney, thank you for taking the time to come back with this response. resolved our issues even though the room mailbox was set to process emails automatically.

[#4]

Thanks, this has resolved for me too... was broken when we added our emails to route OUTBOUND via Mimecast so any mail smart host would also probably break this too.

[#5]

awesome, exactly what I needed! Thank you!!

[#6]

I get this error from any invitation from outside the company, whether it contains a room or not.  Very frustrating.  Why would it not be able to check my own calendar?