extension-dll-exception in User Profile Sync

I have configured User Profile Service.
Previously my user profile synchronization was working fine.

From few days, I am getting "extension-dll-exception" in "DS-DELTASYNC".
When I checked the Stack Trace in Synchronization Service Manager, I am getting the following call stack information.

System.ArgumentException: Item has already been added. Key in dictionary: 'DC=myodc,DC=mydomain,DC=com'  Key being added: 'DC=myodc,DC=mydomain,DC=com'
   at System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add)
   at Microsoft.Office.Server.UserProfiles.MetaverseExtension.MAMetaData.InitializeDomainInfoCache()
   at Microsoft.Office.Server.UserProfiles.MetaverseExtension.MAMetaData.GetDomainValue(ReferenceValue refVal)
   at Microsoft.Office.Server.UserProfiles.MetaverseExtension.MAMetaData.InitializeCSEntry(CSEntry csEntry, MVEntry mvEntry)
   at Microsoft.Office.Server.UserProfiles.MetaverseExtension.MVExtensionObject.Microsoft.MetadirectoryServices.IMVSynchronization.Provision(MVEntry mventry)

I have not changed anything related to User Profile Service.

What could be the problem?