Good day,

In our network at the moment, there are two Exchange Server 07 with last updates and 13cu1, mailboxes were migrated to a new server role owa, activesync, and the others are moved to the new server.
Everything works fine, no errors in the logs, clients are configured. But when looking for some new room mailbox in ECP constantly get the following error:

This mailbox was created successfully, but some properties weren't saved. Close this message, then in the Mailboxes list, double-click this mailbox, set the properties, and click Save.

Cannot open mailbox /o=GXXXXXS/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=EX13SVR01/cn=Microsoft System Attendant.

I repeat, all the logs including the system in the first and second server clean, error-free, box rooms are created but the error I do not like.

Solutions to this problem on the internet (google) is not found. Migration accounts held with no errors.

If anyone encountered this problem, please help me find a solution

PS> pablic folders still on the old server is not migrated.

[PS] C:\Windows\system32>Get-Mailbox -Arbitration

Name                      Alias                ServerName       ProhibitSendQuota
----                      -----                ----------       -----------------
SystemMailbox{1f05a927... SystemMailbox{1f0... EX13SVR01          Unlimited
SystemMailbox{bb558c35... SystemMailbox{bb5... EX13SVR01          Unlimited
SystemMailbox{e0dc1c29... SystemMailbox{e0d... EX13SVR01          Unlimited
Migration.8f3e7716-201... Migration.8f3e771... EX13SVR01          300 MB (314,572,800 bytes)
FederatedEmail.4c1f4d8... FederatedEmail.4c... EX13SVR01          1 MB (1,048,576 bytes)

Thanks for the reply, tried it - seemingly fine.
Room mailbox with ecp and PS created fine and works as it should. But the error that shows ECP looks dangerous that I was very worried.

[PS] C:\Windows\system32>New-Mailbox -Name test2room -room

Name                      Alias                ServerName       ProhibitSendQuota
----                      -----                ----------       -----------------
test2room                 test2room            EX13SVR01          Unlimited

[PS] C:\Windows\system32>