On our ISA system the following warning is logged:

Event Type: Warning
Event Source: Microsoft ISA Server Storage
Event ID: 21326
Description: The ISA Server VSS Writer encountered a failure while backing up 
the ISA Server configuration.

The system configuration is:

  • Windows 2003 Standard SP 2
  • Microsoft ISA 2006 SP 1

Backup agent: EMC NetWorker

Running vssadmin list writers returns

Writer name: "ISA Writer"
Writer Id: {25f33a79-3162-4496-8a7d-caf8e7328205}
Writer Instance Id {f958b2f0-7ad1-4326-9ddc-51aee0ef24c4}
State: [8] Failed
Last error: Retryable error

I'm looking for any hints on what's going wrong here and how I can fix this.


The cause for this issue is that the function CryptSignHash passes AT_SIGNATURE as a parameter. This will fail if the "signature" key pair / certificate is missing. See http://msdn.microsoft.com/en-us/library/aa380280(v=vs.85).aspx

The only supported solution is to set up the machine and ISA Server from scratch.

An unsupported solution ist to create a new key container for ISA.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.