So the NTBackup program creates one big compressed file. And this little workstation/server has far more than 4 Gigabytes of data to backup.

So anyway, the Fujitsu drive comes partitioned with FAT32 which could only handle less than 4GB files sizes. A quick conversion to NTFS

http://technet.microsoft.com/en-us/library/bb456984.aspx

and that fixed that snag.