2012 Essential R2 Backup unsuccessfull with error code 2147942634

Hi, a planned backup on win srv 2012 essentials R2 terminates unsuccessful with error code 2147942634 and the text "more data is abailable" when beginning backup with the EFI start partition. The other, usually follwing backup-locations, do not start backup thereafter. Every 2nd backup seems to be affeted. Manually started backups work fine. Mike.