I have seen this issue when you run Exchange SP1 where the Microsoft VSS writer fails everytime.  the specific error is: 

Backup- Server.server.com-79-57344-34110 – AOFO: Initialization failure on: “\\wedaexch01.kar.wedaskog.se\Microsoft Information Store\First Storage Group”. Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).
Snapshot provider error (0xE000FED1): A failure occurred querying the Writer status.
Check the Windows Event Viewer for details.
Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0×800423f3), State: Failed during prepare snapshot operation (8).
V-79-57344-34110 – AOFO: Initialization failure on: “\\server.server.com\Microsoft Information Store\First Storage Group”. Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).
Snapshot provider error (0xE000FED1): A failure occurred querying the Writer status.
Check the Windows Event Viewer for details.
Writer Name: Exchange Server, Writer ID: {76FE1AC4-15F7-4BCD-987E-8E1ACB462FB7}, Last error: The VSS Writer failed, but the operation can be retried (0×800423f3), State: Failed during prepare snapshot operation (8).
 

If you get this error the first thing to do is open a command prompt and type “VSSADMIN List Writers”  this will give you the VSS writer that failed which should be the Microsoft Exchange VSS writer.

 Writer name: ‘Microsoft Exchange Writer’
   Writer Id: {76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}
   Writer Instance Id: {30bcaa89-69fb-451e-a60d-bf095ca75839}
   State: [8] Failed
  

 Sometimes (but not in this case) certain VSS errors may be resolved by re-registering the operating system’s lower-level VSS components. This step should only be taken after other diagnostics have been failed to correct the failure. To re-register VSS components, execute the following within a command prompt:

cd /d %windir%\system32
net stop vss
net stop swprv
regsvr32 ole32.dll
regsvr32 oleaut32.dll
regsvr32 vss_ps.dll
vssvc /register
regsvr32 /i swprv.dll
regsvr32 /i eventcls.dll
regsvr32 es.dll
regsvr32 stdprov.dll
regsvr32 vssui.dll
regsvr32 msxml.dll
regsvr32 msxml3.dll
regsvr32 msxml4.dll
net start swprv
net start vss

And sometimes you can just reboot, but again, thats not going to fix this one.

Step 1 to fix it is to go to this link:

http://support.microsoft.com/kb/940349 

and download the VSS rollup.  Remember that this must be applied to the backup server as well as the Exchange server.  Once it installs, you will be required to reboot the server.  I have heard people say that they have fixed it simply by doing this but I haven’t seen it yet.

So now on to step 2 which is to  open up the registry editor and navigate to

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem and create a new DWORD

Name: Enable Remote Streaming Backup

Type: DWORD
Value: 1 (remote backup enabled)

This will enable the remote backup and allow the VSS writer and Backup Exec to funtion normally. You need to do this on all Exchange 2007 sp1 servers in your organization.  It is very important to do this and not just install the rollup for VSS.  You will need to reboot after the change!!!

 There is one other thing to check.  If you have recently installed a rollup pack, specifically Rollup 4 for exchange you might need to check the ESE.dll on the backup server and the Exchange server or servers  if they are different copy the newer one and type regsvr32 <path & filename of dll >.

That’s it, you should be up and running again and your information store will be safe and sound.  Again you can upgrade to Backup Exec 12 if you have the money but chances are you just bought Backup Exec 11 a year ago and you don’t want to buy the newest version.  I hope this helps you guys and as always, leave a comment if you have any questions on this fix or any others.