Issue

Bytevault backup of exchange server fails with following error

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[com.ahsay.afc.microsoft.MSExchangeExpt] The writer failed due to an error that would likely not occur if the entire backup, restore, or shadow copy creation process was restarted. (VSS_E_WRITERERROR_RETRYABLE)
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Solution

Volume Shadow Copy Service(VSS) is the service which is responsible for the Backups on your Exchange Server

We can check for available writers using the below command from command prompt.

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Vssadmin list writers
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We could find that some writers are in unstable or in waiting for completion state. "Microsoft Exchange Writer" can be in such a state in many cases.

If "Microsoft Exchange Writer" is unstable or waiting for completion for a long time, the backup is very likely to fail.


Restart of "Microsoft Exchange Information store" Service will help to refresh "Microsoft Exchange Writer" and it may help to resolve the issue.

If restart of  "Microsoft Exchange Information store" Service  is not helping, a server reboot will help to resolve the issue.

If above steps does not help to resolve the issue, we nee to re-register the Vss dlls

Given below commands will help to re-register the VSS dlls

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cd /d %windir%\system32
net stop vss
net stop swprv
regsvr32 /s ole32.dll
regsvr32 /s oleaut32.dll
regsvr32 /s vss_ps.dll
vssvc /register
regsvr32 /s /i swprv.dll
regsvr32 /s /i eventcls.dll
regsvr32 /s es.dll
regsvr32 /s stdprov.dll
regsvr32 /s vssui.dll
regsvr32 /s msxml.dll
regsvr32 /s msxml3.dll
regsvr32 /s msxml4.dll
vssvc /register
net start swprv
net start vss
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Re-registering Volume Shadow Copy Service(VSS) will help to resolve the issue in almost all cases.