Read error on hard drive2

we 've got the latest Version of True Image Echo Server on Server2003 x86 SP2 installed.
and we backuped the all partitions on RDX-Medium
often the fullbackup fails with following error:
Fehler beim Lesen der Festplatte.;Fehler beim Lesen von Sektor 729.050.305 auf Datenträger 2.: Wiederholen/Ignorieren/aLle ignorieren/Abbrechen"
when i edit the Task and open the Source, there harddrive1 - the partitions of the server (c: d: e:)
and the best ist, there another harddrive2 with about 1TB, but there is no other harddrive connect to the Server, also no usb-harddrive
when i restart the Server, the backup is correctly done and the second harddrive in the task isn't there
after 2 weeks, the problem comes the same
as workaround we deinstall Acronis Echo - restart the Server and install Acronis Echo
but it doesn't work
anybody an idea