IMPORTANT: Do NOT use this fix anymore for any SCOM 2012 or SCOM 2012 SP1 or SCOM 2012 R2 instances. In these cases internal processes take care of this. Do NOT create these registry keys unless you really have to. They were used for pre-rtm versions, but not any more for currently used versions.
Microsoft released a KB article for cases where you get this error while running SCOM 2012 on a single management server:
Operations Manager Error: The All Management Servers Pool has not reported availability
You may also see the following events related to the Pool Manager:
Description:
The pool member cannot send a lease request to acquire ownership of managed objects assigned to the pool because half or fewer members of the pool acknowledged the most recent initialization check request. The pool member will continue to send an initialization check request.
Description:
The pool member no longer owns any managed objects assigned to the pool because half or fewer members of the pool have acknowledged the most recent lease request The pool member has unloaded the workflows for managed objects it previously owned.
The related Microsoft KB Article is 2714482 and can be found here http://support.microsoft.com/kb/2714482
To resolve this issue, add the following two Registry keys on the Management Server, under HKLM\System\CurrentControlSet\Services\HealthService\Parameters\PoolManager
Key Type Value
PoolLeaseRequestPeriodSeconds DWORD 600
PoolNetworkLatencySeconds DWORD 120
After doing this, restart the System Center Management Service and the errors should no longer appear.
Very nice B) as in a few smaller environments we have seen these messages before.
Update 22-7-2013: A good addition to this story has been made by Michael in the comments. If you are running multipe management servers in the resource pool and you change the mentioned settings in the registry, make sure you do the same change on all those management servers, so they use the same values. Otherwise other errors will appear.
Update April 2014: Do NOT apply this reg key stuff for SCOM 2012 SP1 or SCOM 2012 R2 anymore. It can cause the oposite effect and make resource pools become more unstable.
Good luck!