Problem Description
During a Druva Phoenix VMware backup or Disaster Recovery (DR) preflight check, the process fails because the failover preflight binary cannot be successfully downloaded or executed on the Windows guest Virtual Machine (VM).
Even though the target virtual machines are active, have sufficient disk capacity (exceeding 1 GB), have functioning VMware Tools, and maintain network connectivity to the Druva cloud, the preflight verification fails despite meeting all basic prerequisites.
Cause
The issue is caused by guest operating system environmental restrictions blocking the Druva backup proxy from injecting or executing the preflight binary:
Windows UAC (User Account Control): Enabled UAC on the guest Windows VM restricts administrative file injection via VMware APIs.
Antivirus/Security Software: Local antivirus software flags or blocks the execution of
PhoenixPreflight_.exe.Network / Firewall Restrictions: * SMB Port (TCP 445) is blocked or disabled, preventing failover preflight binary communication.
Required App-Aware communication ports are restricted between the backup proxy and the VM.
Traceback
The following errors are observed in the backup proxy/drpreflight logs:
level=error ts=2026-04-21T13:08:26.306Z filename=drpreflight.go:173 method=startDRPreflight message="failed to check and download preflight binary" Error="Code: 4295712773, Message: VMware Prerequisites Check: Failed to download failover Prerequisites Check binary, Err: Get \"\": unsupported protocol scheme \"\"" level=error ts=2026-04-21T13:08:19.735Z filename=utils.go:136 method=InjectFile message="failed to inject file in guest" guestOSPath=C:\ProgramData\Druva\EnterpriseWorkloads\vmware\UDA-8453\in.json Error="Failed to upload file in guest after all retries: Failed to upload file to the guest vm"
Resolution
To resolve this issue, ensure the following configurations are met on the target Windows guest VM and network environment:
Disable User Account Control (UAC):
Temporarily deactivate or lower UAC settings within the Windows guest OS to allow the backup proxy to inject the required binaries.
Configure Antivirus Exclusions:
Add an explicit exclusion/whitelist rule in your security software for the executable file:
PhoenixPreflight_.exe.
Verify Guest VM Firewall Rules:
Ensure the local Windows Firewall permits incoming traffic on TCP port 445 (SMB) for preflight failover validation.
Permit incoming traffic via ports 3542 and 3545 if application-aware processing is utilized.
Verify Backup Proxy Routing:
Confirm that the Druva Backup Proxy has unhindered network communication lines with both the vCenter and the guest VM over ports 443, 3542, 3545, and 445.