Acronis Backup 12.5: WinPE bootable media creation fails with "The user attempted to mount to a directory that is not empty. This is not supported."

Symptoms

1. You installed Bootable Media Builder and appropriate Windows AIK/ADK for creating WinPE media.

2. WinPE media creation fails with the following error:

The user attempted to mount to a directory that is not empty. This is not supported.