VSS Service Needed, or not?

Not understanding something I'm seeing-- I'm taking over a few servers and their backups and the task hasn't been handed over gracefully!

We have two practically-identical Exchange mailbox database servers. Even though they have the same database disk size (and database size), one server was running out of space. I found that Volume Shadow Copy was taking up all of the room on this drive so I turned it off since it was already off on the other server. Now, RapidRecovery keeps giving me:

Transfer error

The transfer of one or more volume images from a protected machine to the Core has failed:

* Volume transfer failed: The transfer failed for volume 'D:\'

    * Volume transfer network error: Network error during transfer of data from volume

        * Win32 Api Failed Exception: Failed to open '\\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy354' - The system cannot find the file specified

For the disk I turned Shadow Copy off. I tried creating a new base image and still got the same. Certainly Shadow Copy doesn't have to be enabled for the drive to backup to Rapid Recovery if the other server has it off, no VSS backups, and is backing up still without issue.

Thank you in advance for any assistance here!