error vss writers exchange 2010 windows backup

I have this error, when running windows backup on server with exchange 2010:

Writer name: 'Microsoft Exchange Writer'
   Writer Id: {76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}
   Writer Instance Id: {400de426-a419-459f-a953-91026051bf91}
   State: [8] Failed
   Last error: Retryable error
   
I've rebooted the server several times, but without success.
Does anyone have any idea?

Thank you

Cristiano Ianiri