Exchange Server CCR 2007 unable to see the File Share Witness resulting in mailbox failover ?

Question

Hi people,
Here's my Exchange Server 2007 SP3 in the ideal and normal situation:
Mailbox Server (CCR – Stretched Cluster) Nodes
PRODEXMBX01-VM (Active Mailbox, Quorum) – 10.1.1.53
DREXMBX01-VM (Passive mailbox) – 192.168.1.88
Hub Transport and Client Access Server Nodes
PRODEXHTCAS02-VM – 10.1.1.54
PRODEXHTCAS03-VM (FSW holder) – 10.1.1.55
DREXHTCAS02-VM – 192.168.1.89
Saturday early morning, for some unknown reason the Active Mailbox Server (PRODEXMBX01-VM)
cannot access or see the FSW on the HT server PRODEXHTCAS03-VM, thus
the mailbox gets failover to the DR Mailbox server (DREXMBX01-VM).
Here’s the Events logged:
Log
Name:      System
Source:        Microsoft-Windows-FailoverClustering
Event ID:      1564
Task Category: File Share Witness Resource
Level:Critical
User:          SYSTEM
Computer:      PRODEXMBX01-VM.domain.com
Description:
File
share witness resource 'File Share Witness (\\PRODEXHTCAS03-VM \FSM_DIR_ExMbxCluster01)'
failed to arbitrate for the file share '\\ PRODEXHTCAS03-VM \FSM_DIR_ExMbxCluster01'.
Please ensure that file share '\\ PRODEXHTCAS03-VM \FSM_DIR_ExMbxCluster01'
exists and is accessible by the cluster.
Log Name: System
Source: Microsoft-Windows-FailoverClustering
Event ID:      1177
Task Category: None
Level:       Critical
User:     SYSTEM
Computer:PRODEXMBX01-VM.domain.com
Description:
The Cluster service is shutting down because quorum was lost.
This could be due to the loss of network connectivity between some or all nodes
in the cluster, or a failover of the witness disk.
Run
the Validate a Configuration wizard to check your network configuration. If the
condition persists, check for hardware or software errors related to the
network adapter. Also check for failures in any other network components to
which the node is connected such as hubs, switches, or bridges.
So I had to perform manual failover back from DR to production so that both Active mailbox and the Quorum
are held by the Production Mailbox server (PRODEXMBX01-VM).
On Sunday Morning, the Event ID Critical 1564 occurred again thus causing only the quorum only to failover
to the DR mailbox server (DREXMBX01-VM) but the Active mailbox role is still held by the Production Exchange server (PRODEXMBX01-VM). 
So now the situation is like the following:
Mailbox Server (CCR – Stretched Cluster) Nodes
PRODEXMBX01-VM (Active Mailbox) – 10.1.1.53
DREXMBX01-VM (Passive mailbox, Quorum) – 192.168.1.88
Hub Transport and Client Access Server Nodes
PRODEXHTCAS02-VM – 10.1.1.54
PRODEXHTCAS03-VM (FSW holder) – 10.1.1.55
DREXHTCAS02-VM – 192.168.1.89
So what causing the mailbox servers unable to contact the File Share Witness?
/* Server Support Specialist */

Answer 1

Did you check the blog above? 
The account used in the clustered machine should have access to
\\PRODEXHTCAS03-VM\FSM_DIR_ExMbxCluster01. Please check the permissions. Try giving full permission to admins as well (just to try)
MAS
I've followed this (http://technet.microsoft.com/en-us/library/bb124922(v=exchg.80).aspx) instruction and there is no mentioning other than the Cluster Service Account. 
/* Server Support Specialist */