Solution how to fix error with Managed Metadata service in Share­Point 2013:

• Error in Central Adminis­tra­tion: The Managed Metadata Service or Connec­tion is currently not available
• Excep­tion in ULS: KeyNot­Found­Ex­cep­tion The given key was not present in the dictionary

Recently I got his error when I tried to work in the Managed Metadata service appli­ca­tion in Share­Point 2013:

The Managed Metadata Service or Connec­tion is currently not available. The Appli­ca­tion Pool or Managed Metadata Web Service may not have been started. Please Contact your Administrator

The ULS log shows:
Failed to get term store for proxy ‘Managed Metadata Service Appli­ca­tion Proxy’. Excep­tion: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
at Microsoft.SharePoint.Taxonomy.Internal.XmlDataReader.GetDateTime(String name)
at Microsoft.SharePoint.Taxonomy.Internal.SharedTermStore.Initialize(IDataReader dataReader, Guid termS­to­reIdValue, Boolean fromPersistedData)
at Microsoft.SharePoint.Taxonomy.Internal.SharedTermStore..ctor(IDataReader dataReader, Guid termS­to­reId, Boolean fromPersistedData)
at Microsoft.SharePoint.Taxonomy.Internal.DataAccessManager.GetTermStoreData

(Metada­ta­Web­Ser­vice­Ap­pli­ca­ti­on­Proxy shared­Ser­vice­Proxy, Boolean& partitionCreated)

After some trouble­shoo­ting, we’re able to fix the issue:

- Backup database of Managed Metadata service
— Delete the existing Managed Metadata service appli­ca­tion (without deleting the database)
— Create a new Managed Metadata service appli­ca­tion with new database
— Edit the proper­ties of the new Managed Metadata service appli­ca­tion, point to the original database
— iisreset
— The Manage Metadata Service was back again

Good luck!