Acronis products currently do not support backing up of locally mapped disks using the subst utility
Update to the latest build or unmap unavailable drives
Why saving an image to a mapped drive may sometimes fail
Deployment fails because there is no disk at all, Acronis Linux fails to detect it, or there is not enough free space
This article applies to:
Acronis True Image 2015/2014
Acronis Cloud supports backup from the following sources:
Mapped drives are not listed/available in GUI (e.g. as the backup source/destination) or backup via acrocmd command line tool to a mapped drive fails.