Ghost 12: Device \\.\SymantecSnapshot9 cannot read 8192 sectors starting at LBA 2017520.

During a backup I got the following error message:

 

-Error E7C3000F: Device \\.\SymantecSnapshot9 cannot read 8192 sectors starting at LBA 2017520.

--Error EBAB03F1: The request could not be performed because of an I/O device error.

According the "Help on the web", this is an unknown error.

What is the matter?