Microsoft issued another clustering update for Windows Server 2008 R2. This one is where:
The Cluster service still uses the default regroup time-out value of 6 seconds after you configure the regroup time-out setting on a computer that is running Windows Server 2008 R2. This time-out value may not be long enough for some cluster nodes to rejoin a large scale cluster after you restart the Cluster service.
Note To obtain the time-out value (ClusSvcRegroupOpeningTimeout), type the following command at a command prompt, and then press Enter:
Microsoft says you can fix this by Installing the available hotfix.
After you install the following hotfix package, the following regroup settings become effective: