Cannot open mailbox system attendand- randomly

Question

Hello,
our environment have Exchange 2013 with CU7 installed, and lately receive weird problem that is not persistent but it unexplained.
All databases mounted that are in DAG, all arbitration mailboxes good, in ADSIEDIT checked homeMDB, and it is not set, however, i dont know is this relevant because sometimes is failing, sometimes is success.
When we run user creation we randomly get error:
Cannot open mailbox /o=ORGANIZATION/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=SERVER/cn=Microsoft System Attendant. CategoryInfo: NotSpecified: (:) [Set-MailboxRegionalConfiguration],
MailboxUnavailableException, FullyQualifiedErrorId: [Server=SERVER,RequestId=ba479b62-bda0-4c55-9347-9279f6121d62,TimeStamp=3/18/2015 7:57:29 PM] [FailureCategory=Cmdlet-MailboxUnavailableException] 45AC6FDA,Microsoft.Exchange.Management.StoreTasks.SetMailboxRegionalConfiguration
Googled many answers, tried many workarounds, and I'm out of ideas now, so any suggestion will be more than welcome!
Thanks,
Ivica

Answer 1

Well, i would do that, except that Exchange 2013 don't have System attendant service.
Also, we have 6 databases, how do i know which one to put in homeMDB field?
I did as you instructed anyway for test and still receive error:
<?xml version="1.0"?>
<Objects>
  <Object Type="System.Management.Automation.PSCustomObject">
    <Property Name="message" Type="System.String">Can't create user</Property>
    <Property Name="detailMessage" Type="System.String">Cannot open mailbox /o=secureemail/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=SERVER/cn=Microsoft System Attendant. CategoryInfo:
NotSpecified: (:) [Set-MailboxRegionalConfiguration], StorageTransientException, FullyQualifiedErrorId: [Server=SERVER,RequestId=557e3eb8-ddbb-44c9aab1-d18c0682beb5,TimeStamp=3/19/2015 2:45:32 PM] [FailureCategory=Cmdlet-StorageTransientException] 2CC71ED6,Microsoft.Excha
nge.Management.StoreTasks.SetMailboxRegionalConfiguration</Property>
    <Property Name="responseCode" Type="System.String">400</Property>
  </Object>
</Objects>
Keep in mind that servers are in remote AD sites, replication and AD health is good!
This is script that is failing:
$ErrorActionPreference = "Stop";
try{
Add-PSSnapin Microsoft.Exchange.Management.PowerShell.SnapIn
$OrganizationName = "[email protected]" #User defined mail address
$organizationUnit = "OU=$OrganizationName,OU=users,DC=domain,DC=priv";
$name = "John"                                            
#this should be asked in web interface (firstname)
$lastname = "Dpe"                                              
#this should be asked in web interface (lastname)
$displayName = "John Doe" # this is display name in OWA and in all address books
$logonName = "john"    # this will be users choosen logon name (before @externaldomain.com)
$ExternalDomain = "example.com"        #this value user will enter as his wanted username and will use it together with his external domain name [email protected]
$UPN = "$LogonName@$ExternalDomain"   #this should remain to be done automatically and under assumption domain is provisioned!!
$DomainController = "server"   #this value must be specified based on domain controller in AD site where user will be created
$nonadmin = "$OrganizationName All Users"; #This is field for entire tenant management and members are used for calendar sharing
$database = "database"                               
$retentionPolicy = "DoNotRemove"
$customattribute1 = "$OrganizationName" #Add for possible manipulation of tenants for future need
$customattribute2 = "ServiceID"
$customattribute3 = "ContactID"
$customattribute4 = "ClientID"
$password =ConvertTo-SecureString 'Password123' -AsPlainText -Force
$mailbox = New-Mailbox -DomainController "$DomainController" -RetentionPolicy $retentionPolicy -UserPrincipalName $UPN -Name "$name $lastname" -OrganizationalUnit "$organizationUnit" -Password $password -FirstName "$name"
-LastName "$lastname" -Displayname "$Displayname" -database $database -ResetPasswordOnNextLogon $false  #This is part where user is created
Start-Sleep -s 2;
Add-DistributionGroupMember -Identity "$nonadmin" -Member "$UPN" -BypassSecurityGroupManagerCheck  -DomainController "$DomainController"      #at this line user is placed in distribution group and
that group is used for additional security
Start-Sleep -s 2;
Set-Mailbox -AddressBookPolicy "$OrganizationName ABP" -Identity "$UPN" -DomainController "$DomainController" #from this point user gets his address book and isolation part.
Set-Mailbox -Identity "$UPN" -DomainController "$DomainController" -EmailAddressPolicyEnabled:$False #disables force of address policy
Set-Mailbox -identity "$UPN" -PrimarySmtpAddress  $UPN  -DomainController "$DomainController" ; #assigns default mail address
Start-Sleep -s 2;
Set-CASMailbox -identity "$UPN" -OwaMailboxPolicy Default  -DomainController "$DomainController" #In this policy it is defined that user cant manage his password, as any future change will be managed globally here and automatically
applied to all users
Set-MailboxRegionalConfiguration -Identity "$UPN" -Language en-us -DomainController "$DomainController" -Confirm:$False
Set-MailboxFolderPermission -identity ${UPN}:\calendar -User default -accessrights none -DomainController "$DomainController"   
add-MailboxFolderPermission -Identity ${UPN}:\calendar -user "$nonadmin" -AccessRights AvailabilityOnly -DomainController "$DomainController"    #only members of classic users can see free/busy
set-mailbox -identity $UPN -customattribute1 $customattribute1 -customattribute2 $customattribute2 -customattribute3 $customattribute3 -customattribute4 $customattribute4 -DomainController "$DomainController"
$mailbox | Set-CasMailbox -DomainController "$DomainController" -ActiveSyncEnabled $true -PopEnabled $true -ImapEnabled $true -OWAEnabled $true -MAPIEnabled $true; #adding script for created user to be returned after creation