If you want to perform any (not only backup operations) using a network drive, you have two options:
1. The network drive should already be connected.
2. R-Drive Image can start a batch file to connect the drive before the operation and, if necessary, disconnect the drive after the operation.
The batch file should be specified in the Backup AUX applications option on the Backup Options Panel.
This article explains which commands to use to create such butch files: How to Map Network Drives From the Command Prompt in Windows