MapError: unknown Mac error -5000

Hello, could someone advise me on what the -5000 error may be below.

The Mac OS X Server 10.7.3 on a Mac Pro is working fine with all these files on this external Lacie 8TB Enterprise Raid 'CORE RAID 2', seems to only be Retrospect with the problem.

Thank you,

+ Normal backup using WK02 INC at 21/07/2012 (Activity Thread 1)
To Media Set WK02...
- 21/07/2012 11:13:51: Copying CORE RAID
MapError: unknown Mac error -5000
22/07/2012 01:07:25: Snapshot stored, 51.8 MB
22/07/2012 01:07:29: Execution completed successfully
Completed: 128926 files, 2,100.2 GB
Performance: 2,595.7 MB/minute
Duration: 13:53:37 (00:05:05 idle/loading/preparing)
- 22/07/2012 01:07:29: Copying CORE RAID 2
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
MapError: unknown Mac error -5000
22/07/2012 19:05:47: Snapshot stored, 172.1 MB
22/07/2012 19:05:54: Execution completed successfully
Completed: 258280 files, 2,769.4 GB
Performance: 2,640.7 MB/minute
Duration: 17:58:25 (00:04:34 idle/loading/preparing)
22/07/2012 19:08:20: Execution completed successfully
Total performance: 2,617.8 MB/minute
Total duration: 07:52:02 (00:09:39 idle/loading/preparing)