failed grooming (out of disk space) + failed catalog rebuild

[Toranaga1866]

My specs:

 

Windows XP sp2 running Retrospect

2 Raid drives running daily backups (1.5 TB, and 1TB)

2 1.5TB external Maxtor hard drives running weekly offsite backups

 

Issue:

 

Once a week I run a snapshot transfer of the latest daily backups to an external hard drive which I alternate every week. One of the external hard drives (known as Cronk) was down to 50Gb of disk space so I decided to manually run a groom to clear all but the last 2 snapshots off the disk. A while into the execution (over an hour I'd guess) the external hard drive RAN OUT OF DISK SPACE!!! It then told me i had to run a catalog rebuild on the backup set for the external hard drive (let it be known that there are 2 backup sets that point to Cronk, both are allowed 99% disk usage), but when I try to run the catalog rebuild from the data on the external hard drive I get this error:

 

"The Backup Set data file name is invalid, cannot recatalog the set using these files."

 

Question 1: why did the groom fill the hard drive instead of clean it?

 

Question 2: why is are my attempts at a catalog rebuild failing before they begin?

 

Any/all input is much appreciated!