Exchange 2010 / 2013 meetings with rooms stopped working

Our client had a little problem today where after patching of all Exchange 2010 / 2013 servers users started noticing weird issues with Meeting Requests and Room Mailboxes in particular. 

There were several issues noticed by multiple users:

no confirmation for meeting is sent / received by meeting rooms

internal apps for scheduling rooms timing out

users not able to schedule new meetings with resource mailboxes

users not able to postpone meetings with resource / room mailboxes (getting access denied)

adding new meetings ends with error access denied to create elements in folder

removing meeting request with resource mailboxes doesn't work

Since there was only one thing in common we decided to do 2 things:

Move arbitration mailboxes to different databases

Move databases in DAG to their counter-part servers

Both those actions helped to resolve the problem and users were able to work with meetings again. Below you can find quick steps:

[PS] C:\>get-mailbox -arbitration | fl name,database

Name     : SystemMailbox{1f05a927-a1fd-4ef6-96aa-50f419d0d2b7}
Database : MDB01

Name     : FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
Database : MDB01

Name     : SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}
Database : MDB01

Name     : SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c}
Database : MailboxDatabase2

Name     : Migration.8f3e7716-2011-43e4-96b1-aba62d229136
Database : MailboxDatabase2

Move mailboxes on Exchange 2013 from MailboxDatabase2 to MailboxDatabase1

[PS] C:\>get-mailbox -Arbitration -Database MailboxDatabase2 | New-MoveRequest -TargetDatabase MailboxDatabase1

DisplayName                              StatusDetail              TotalMailboxSize
-----------                              ------------              ----------------
Microsoft Exchange                       Queued                    1.098 MB (1,151,522 bytes)
Microsoft Exchange Migration             Queued                    255.2 KB (261,300 bytes)

Move mailboxes on Exchange 2010 from MDB01 to MDB02

[PS] C:\Windows\system32>get-mailbox -Arbitration -Database MDB01 | New-MoveRequest -TargetDatabase MDB02

DisplayName                              Status                    TotalMailboxSize
-----------                              ------                    ----------------
Microsoft Exchange Approval Assistant    Queued                    2.575 KB (2,637 bytes)
Microsoft Exchange Federation Mailbox    Queued                    0 B (0 bytes)
Microsoft Exchange                       Queued                    5.042 MB (5,287,193 bytes)

Then quickly check on progress

[PS] C:\Windows\system32>Get-MoveRequest

DisplayName                              Status                    TargetDatabase
-----------                              ------                    --------------
Microsoft Exchange                       Queued                    MDB02
Microsoft Exchange                       InProgress                MailboxDatabase1
Microsoft Exchange Migration             InProgress                MailboxDatabase1
Microsoft Exchange Approval Assistant    CompletionInProgress      MDB02
Microsoft Exchange Federation Mailbox    CompletionInProgress      MDB02

And when it's done, wait for propagation to happen (depending on size of your organization it may be quick or not) and restart Outlook to make sure Outlook is aware of the change (faster then usually). If you don't want to risk if it solved your issue or not you can make the switch in DAG databases to move DB's between servers but those simple steps described above should solve the issue without need for touching DAG and replication of databases.