exchange periodicly looses connection to ADS

hi there

my exchange 2007 periodicly looses it connection to the Active Directory.
when the connection is lost, the clients can't login. this hapes once a day.

i see the following events in the event log:


Log Name:      Application
Source:        MSExchange ADAccess
Date:          21.05.2009 15:04:24
Event ID:      2102
Task Category: Topology
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      rh-msx-s01.sbw.global
Description:
Process MAD.EXE (PID=2972). All Domain Controller Servers in use are not responding:
rh-dc-s01.sbw.global
rh-dc-s02.sbw.global
kr-dc-s01.sbw.global
kr-dc-s02.sbw.global


Log Name:      Application
Source:        MSExchange RPC Over HTTP Autoconfig
Date:          21.05.2009 15:04:31
Event ID:      2001
Task Category: General
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      rh-msx-s01.sbw.global
Description:
An error has occurred. The problem may resolve itself. The service will retry the operation in 15 minutes. Message:

Active Directory operation failed on rh-dc-s01.sbw.global. This error could have been caused by user input or by the Active Directory server being unavailable. Please retry at a later time. Additional information: Active directory response: The operation was aborted because the client side timeout limit was exceeded. .


 
Log Name:      Application
Source:        MSExchangeMailboxAssistants
Date:          21.05.2009 15:05:50
Event ID:      10003
Task Category: Managed Folder Assistant
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      rh-msx-s01.sbw.global
Description:
Could not get the server configuration object from Active Directory. Microsoft.Exchange.Assistants.ServerIneptException ---> Microsoft.Exchange.Data.Directory.ADPossibleOperationException: Active Directory operation failed on rh-dc-s01.sbw.global. This error could have been caused by user input or by the Active Directory server being unavailable. Please retry at a later time. Additional information: Active directory response: The operation was aborted because the client side timeout limit was exceeded. . ---> System.DirectoryServices.Protocols.LdapException: The operation was aborted because the client side timeout limit was exceeded.
   at System.DirectoryServices.Protocols.LdapConnection.ConstructResponse(Int32 messageId, LdapOperation operation, ResultAll resultType, TimeSpan requestTimeOut, Boolean exceptionOnTimeOut)
   at System.DirectoryServices.Protocols.LdapConnection.SendRequest(DirectoryRequest request, TimeSpan requestTimeout)
   at Microsoft.Exchange.Data.Directory.PooledLdapConnection.SendRequest(DirectoryRequest request, LdapOperation ldapOperation)
   at Microsoft.Exchange.Data.Directory.ADSession.Find(ADObjectId rootId, String optionalBaseDN, ADObjectId readId, QueryScope scope, QueryFilter filter, SortBy sortBy, Int32 maxResults, IEnumerable`1 properties, CreateObjectDelegate objectCreator, CreateObjectsDelegate arrayCreator)
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.Data.Directory.ADSession.AnalyzeDirectoryError(PooledLdapConnection connection, DirectoryRequest request, DirectoryException de, Int32 totalRetries, Int32 retriesOnServer)
   at Microsoft.Exchange.Data.Directory.ADSession.Find(ADObjectId rootId, String optionalBaseDN, ADObjectId readId, QueryScope scope, QueryFilter filter, SortBy sortBy, Int32 maxResults, IEnumerable`1 properties, CreateObjectDelegate objectCreator, CreateObjectsDelegate arrayCreator)
   at Microsoft.Exchange.Data.Directory.ADSession.Find(ADObjectId rootId, QueryScope scope, QueryFilter filter, SortBy sortBy, Int32 maxResults, IEnumerable`1 properties, CreateObjectDelegate objectCtor, CreateObjectsDelegate arrayCtor)
   at Microsoft.Exchange.Data.Directory.ADSession.Find[TResult](ADObjectId rootId, QueryScope scope, QueryFilter filter, SortBy sortBy, Int32 maxResults, IEnumerable`1 properties)
   at Microsoft.Exchange.Data.Directory.SystemConfiguration.ADSystemConfigurationSession.Find[TResult](ADObjectId rootId, QueryScope scope, QueryFilter filter, SortBy sortBy, Int32 maxResults)
   at Microsoft.Exchange.Data.Directory.SystemConfiguration.ADSystemConfigurationSession.FindServerByFqdn(String serverFqdn)
   at Microsoft.Exchange.Data.Directory.SystemConfiguration.ADSystemConfigurationSession.FindLocalServer()
   at Microsoft.Exchange.InfoWorker.Assistants.ExchangeServer.<>c__DisplayClass2.<TryGetServer>b__0()
   at Microsoft.Exchange.Assistants.Util.<>c__DisplayClass2.<CatchMeIfYouCan>b__0()
   --- End of inner exception stack trace ---
   at Microsoft.Exchange.Assistants.Util.CatchMeIfYouCan(CatchMe function)
   at Microsoft.Exchange.InfoWorker.Assistants.ExchangeServer.TryGetServer(). Check for domain controller network connectivity issues or incorrect DNS configuration.


the exchange server is configured to store it's configuration on rh-dc-s01.sbw.global

when the connection is lost, i have to reboot the server. then everything works fine for a day.

has anyone experienced something like this? any ideas? how do i troubleshoot this?

thanks,
tobias