Outlook 2010 Problem opening shared mailbox "the set of folders cannot be opened. Microsoft Exchange is not available"

Question

Hi, I have a number of mailboxes configured for sharing.
For those users who have full access rights (given via EMC) the mailboxes automatically appear in Outlook 2010.
However for one of those mailboxes the users recieve the following error when they try to access it:
"The Set of Folders cannot be opened. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance."
Meanwhile the users' primary mailboxes continue to work as normal, as do the other mailboxes that have been shared with them.
The output of get-mailboxpermissions for the problematic mailbox is the same as the output for a full working one.
If I add the mailbox to my account (as though I was using Outlook 2003) it allows me access, however I then have the situation of having the mailbox listed twice, one working the other not.
How do I get this mailbox to behave as expected?
Many thanks
Nick

Answer 1

So the problem returns. I'm not sure what we did to work around it, the users who were having the problem have left and the new batch are now encountering it.
I have issued the following command on the Exchange Server (one site, one server, all roles, only a default throttling policy exists):
$a = Get-ThrottlingPolicy | where-object {$_.IsDefault -eq $true}
$a | Set-ThrottlingPolicy -RCAMaxConcurrency 40
The result of Get-ThrottleingPolicy is:
RunspaceId                                : 8bc47cdf-a695-47f0-b31e-e6ffba6aed66
IsDefault                                 : True
AnonymousMaxConcurrency                   : 1
AnonymousPercentTimeInAD                  :
AnonymousPercentTimeInCAS                 :
AnonymousPercentTimeInMailboxRPC          :
EASMaxConcurrency                         : 10
EASPercentTimeInAD                        :
EASPercentTimeInCAS                       :
EASPercentTimeInMailboxRPC                :
EASMaxDevices                             : 10
EASMaxDeviceDeletesPerMonth               :
EWSMaxConcurrency                         : 10
EWSPercentTimeInAD                        : 50
EWSPercentTimeInCAS                       : 90
EWSPercentTimeInMailboxRPC                : 60
EWSMaxSubscriptions                       : 5000
EWSFastSearchTimeoutInSeconds             : 60
EWSFindCountLimit                         : 1000
IMAPMaxConcurrency                        :
IMAPPercentTimeInAD                       :
IMAPPercentTimeInCAS                      :
IMAPPercentTimeInMailboxRPC               :
OWAMaxConcurrency                         : 5
OWAPercentTimeInAD                        : 30
OWAPercentTimeInCAS                       : 150
OWAPercentTimeInMailboxRPC                : 150
POPMaxConcurrency                         : 20
POPPercentTimeInAD                        :
POPPercentTimeInCAS                       :
POPPercentTimeInMailboxRPC                :
PowerShellMaxConcurrency                  : 18
PowerShellMaxTenantConcurrency            :
PowerShellMaxCmdlets                      :
PowerShellMaxCmdletsTimePeriod            :
ExchangeMaxCmdlets                        :
PowerShellMaxCmdletQueueDepth             :
PowerShellMaxDestructiveCmdlets           :
PowerShellMaxDestructiveCmdletsTimePeriod :
RCAMaxConcurrency                         : 40
RCAPercentTimeInAD                        : 5
RCAPercentTimeInCAS                       : 205
RCAPercentTimeInMailboxRPC                : 200
CPAMaxConcurrency                         : 20
CPAPercentTimeInCAS                       : 205
CPAPercentTimeInMailboxRPC                : 200
MessageRateLimit                          :
RecipientRateLimit                        :
ForwardeeLimit                            :
CPUStartPercent                           : 75
AdminDisplayName                          :
ExchangeVersion                           : 0.10 (14.0.100.0)
Name                                      : DefaultThrottlingPolicy_eccf5379-4fb6-4e97-8b47-37b1dc58a9
DistinguishedName                         : CN=DefaultThrottlingPolicy_eccf5379-4fb6-4e97-8b47-37b1dc5
ettings,CN=Our Org Name,CN=Microsoft Exchange
onfiguration,DC=domain,DC=internal
Identity                                  : DefaultThrottlingPolicy_eccf5379-4fb6-4e97-8b47-37b1dc58a9
Guid                                      : a274d3ec-f2f8-43c3-ad26-6b960924ef0e
ObjectCategory                            : domain.internal/Configuration/Schema/ms-Exch-Throttling-Polic
ObjectClass                               : {top, msExchGenericPolicy, msExchThrottlingPolicy}
WhenChanged                               : 07/06/2011 10:24:47
WhenCreated                               : 07/06/2011 10:24:41
WhenChangedUTC                            : 07/06/2011 09:24:47
WhenCreatedUTC                            : 07/06/2011 09:24:41
OrganizationId                            :
OriginatingServer                         : OneOfTheDCs.domain.internal
IsValid                                   : True
But the problem remains. Do I need to adjust anything else for this value (40) to become active? The documentation implies that the above is required on a CAS, however there is mention of registry settings but no guidance on whether these are required if
the above is used.
When I create a second profile via Mail (in control panel) for the shared mailbox and then start outlook using this profile I am able to access the mailbox as expected. This is running in the context of the user who cannot access it from her
default Outlook profile.
Many thanks