Multiple backups to Multiple USB attached drives

OK, I have been doing a lot of reading on this subject but still don't have a good answer to my question and I'm hoping someone can give me a good workaround to my problem.

I have two servers that I'm backing up. Both have their own copy of Acronis Backup 11.5 for WIndows because they are at different locations.

This is the setup:

USB 3.0 attached HD Dock at both locations.
Multiple 1Gb SATA HDs for the docks
Main site server takes about 400Gb per backup
Sister site takes about 200Gb per backup.

At the sister site I set retention rules on the backups to only hold (max backups available on 1 drive - 1).
At the main site I set retention rules on the backups to only hold 1 backup.
The cleanup is set to run before the backup.

This is the result at the sister site when the 4th backup tries to run:

Error code: 61
Module: 309
LineInfo: 4a8728dc8a1c950f
Fields: $module : service_process_vs_39029
Message: Command 'Replicating backups/cleaning up archives (1st location)' has failed.
--------------------
Error code: 218
Module: 161
LineInfo: b320396adfe3ccb
Fields: IsReturnCode : 1, $module : disk_bundle_vs_39029
Message: Failed to delete the backups from archive 'K:\Acronis\#arl:/BC7897B0-F69C-4F98-916D-0DFE6B14485B/66D108D2-C32E-43CC-A195-23E85239D9BB/7A6482DF-904E-4837-8072-038537FFE344?archive_name%3dDailyMWF' by the specified filter.
--------------------
Error code: 507
Module: 64
LineInfo: a1d3981537c687bf
Fields: id : DailyMWF_2014_10_27_20_01_27_219D.TIB, $module : disk_bundle_vs_39029
Message: Failed to open the backup archive by the ID.
--------------------
Error code: 1
Module: 64
LineInfo: 98130db273d2480
Fields: $module : disk_bundle_vs_39029
Message: The archive is invalid or its type is unsupported.
--------------------
Error code: 9
Module: 64
LineInfo: 95962d9a14426d33
Fields: $module : disk_bundle_vs_39029
Message: Failed to find the backup.
--------------------
Error code: 9
Module: 64
LineInfo: 95962d9a14426d33
Fields: $module : disk_bundle_vs_39029
Message: Failed to find the backup.

I assume this is because the backup archive in question is on another drive and the software can't find it? It's like the software is treating the vault as one large vault and not vaults on separate drives?

How do I fix this? I want to keep the maximum amount of backup history that I'm purchasing drive space for but I'm having trouble getting the result that I want.

I was using the retention rule that said remove when device full, and was having sporadic results with it also.

This software costs $1500 and it can't seem to handle what I'm trying to do. Very unacceptable.

I use Macrium Reflect software on another server (different client) that cost $300 and it does exactly what I want it to do. No problems whatsoever.

What gives... I don't want to throw away $3000 worth of software and then purchase $600 to get reliable backups for my client.

Thanks for any help you can give me!