I posted here last week with the same problem. All of my backups regardless 
of what I'm backing up fail with the following:

DPM encountered a critical error while performing an I/O operation on the 
tape Daily & Weekly  User Data, Shared Areas-00000007 (COP159L3) (Barcode - 
COP159L3) in Drive Quantum LTO 3 Tape Drive. (ID 30101 Details: The request 
could not be performed because of an I/O device error (0x8007045D))

I have applied all of the updates (which was the suggestion from my last 
post) but this didn't make a scrap of difference.
I am running DPM 2007 on Windows server 2008 64bit with a Quantum 
Superloader 3 and a LTO 3 tape drive.
I took the superloader to another location which has exactly the same set up 
and it worked fine, so proves the superloader works.
I swapped out the SCSI cable too as a last desperate attempt and that didn't 
work either.

Has anyone please got any suggestions on what to try next as we are 
currently without a backup solution and have been for two weeks!

        This library is tested with the following driver set, can you please 
give it a try if possible? Here is a full list of DPM tested libraries:
http://technet.microsoft.com/en-us/systemcenter/dm/cc678583.aspx. We are 
trying to get a tool verify weather a tape library can be used with DPM or 
not, that could help isolating the issue with DPM/Tape library(or its 
drivers).

Superloader 3 QsmcX32.sys, 2/15/2005, 2.0.4.0, unsigned, 32bit
qsmcx64.sys, 7/8/2008, 2.5.1.0, signed, 64bit V30.0
V61  LTO-3
SDLT600 ViperW2k.sys, 8/26/2004, 1.9.0.0, signed, 32bit
qdltx64.sys, 1/10/2008, 4.5.1.0, signed, 64bit 1794
V51

Thanks,
Praveen D [MSFT]
This posting is provided "AS IS" with no warranties, and confers no rights.

"Katrina" <Katrina@discussions.microsoft.com> wrote in message 
news:5B1B4E01-86BF-4C86-BEC7-78C7F7E981C3@microsoft.com...
> I posted here last week with the same problem. All of my backups 
> regardless
> of what I'm backing up fail with the following:
>
> DPM encountered a critical error while performing an I/O operation on the
> tape Daily & Weekly  User Data, Shared Areas-00000007 (COP159L3) 
> (Barcode -
> COP159L3) in Drive Quantum LTO 3 Tape Drive. (ID 30101 Details: The 
> request
> could not be performed because of an I/O device error (0x8007045D))
>
> I have applied all of the updates (which was the suggestion from my last
> post) but this didn't make a scrap of difference.
> I am running DPM 2007 on Windows server 2008 64bit with a Quantum
> Superloader 3 and a LTO 3 tape drive.
> I took the superloader to another location which has exactly the same set 
> up
> and it worked fine, so proves the superloader works.
> I swapped out the SCSI cable too as a last desperate attempt and that 
> didn't
> work either.
>
> Has anyone please got any suggestions on what to try next as we are
> currently without a backup solution and have been for two weeks!