Avamar 7.1: Backups fail with "Internal Error: backtree: bad response"

I have a new Avamar 4S grid running 7.1 sending data to a Data Domain running v5.5.  I am trying to back up three Windows secondary domain controllers / file servers, which are at remote sites (all 50+ miles from my datacenter).  All three of these used to back up to my old Gen3 grid (which ran 7.0) without any issues.  Since trying to convert them to the new grid, they all fail during scheduled backups with the following errors:

2014-12-08 18:45:57 avtar Info <7694>: Server(avamarutil) not responding (possible network congestion?) (300 seconds)

2014-12-08 18:50:52 avtar Error <5775>: Internal Error: backtree: bad response 48df4c612d23a6d5f1af0462ea12188b95695b29 14113 ADD_HASH_DATA=2 serial=14113 seq=0 flags=R:N:0 kind=9 rsp=MSG_ERR_INVALID_PARAMETERS
2014-12-08 18:50:52 avtar Info <5726>: Aborting backup due to error (3:EXC_HFSERROR)
2014-12-08 18:50:53 avtar Info <7695>: Server(avamarutil) is back (591 seconds)
2014-12-08 18:50:54 avtar FATAL <5399>: Internal error, aborting
2014-12-08 18:50:54 avtar Info <9772>: Starting graceful (staged) termination, error reported in nbackmain (wrap-up stage)
2014-12-08 18:50:54 avtar Info <7883>: Finished at 2014-12-08 18:50:54 Mountain Standard Time, Elapsed time: 0000h:50m:53s
2014-12-08 18:50:54 avtar Info <17971>: Errors, cancellation or termination caused the backup to not be posted on the DDR
2014-12-08 18:50:54 avtar Info <12530>: Backup was not committed to the DDR.

These clients work fine when I do on-demand backups, though I've never tried doing an on-demand backup of the entire server.  Given the distance and the fact that the network connectivity to the remote clients isn't the best, I expect there to be times when there may be congestion.  In the logs, it always has the line about the utility server being back around 590 seconds.  I've read other posts and in the documentation where it says that the 300 seconds is a default.

Is there somewhere I can change that value to give these clients more time to re-establish a connection if it fails or becomes busy?  Or am I barking up the wrong tree here for a resolution to this problem?

Thank you,

Waide R. Yokom