Veeam Backup – Failed to prepare guests for volume snapshot

Error
Processing <VM-Name> Error: Failed to prepare guests for volume snapshot.
Unable to subscribe to guest processing components: Cannot do HvPrepareSnapshot. Error: Failed to inject VSS plug-in. VirtualAlloc failed Win32 error:Access is denied. Code: 5
Failed to create VM recovery checkpoint (mode: Veeam application-aware processing) Details: Failed to prepare guests for volume snapshot.
Error: Failed to prepare guests for volume snapshot.You may receive about error while trying to backup Virtual Machines from Veeam Backup. There are many suggestions and fixes are available in the internet, however we have come across a different scenario for the same issue.

Suggestion 01: Check for Volume Shadow Copy errors on both Host and Guest Virtual Machines.

1. Open Command Prompt with Administrative privileges.
2. Run “vssadmin list writers”
3. Check the state of all the Writers.

Suggestion 02: Check the credentials on Guest OS. (For AAP – Application Aware Processing)

1. Edit the Backup Job.
2. Go to “Guest Processing”
3. Check the assigned credentials and test.

In our case we couldn’t find any issues on VSS Writers or AAP. But we noticed that “VeeamGuestHelper.exe” has been blocked by the Endpoint Protection Software.

Once we excluded the application (C:\Windows\VeeamVssSupport\VeeamGuestHelper.exe) from the endpoint the backup started to complete without any issue.