See bug at: http://www.cisco.com/pcgi-bin/Support/Bugtool/onebug.pl?bugid=CSCse49574
Apparently, Cisco doesn't know why it happens to some and not to others and there is no way to prevent running into it. When attempting to load OS 2000.4.3(a) on a supported MCS-7825-H2 or the like, everything will proceed until the image is copied o the disk(s). The copy will fail and you'll have to begin the process again.
You can simply keep retrying (it may take a dozen attempts) and ultimately it will work, or follow the steps on the link re: trashing the RAID array. If that doesn't work:
"If perform all of the above steps and this has not resolved the issue, I have also seen it resolved by performing a System Erase from the HP SmartStart CD menu options (when booted from), prior to installing. If you do not have a SmartStart CD, you may be able to perform a similar action in the BIOS menu (F9 on boot-up) to Erase NVRAM/Boot Disk in the Advanced Options sub-menu. "