Hi,
It's likely some sort of unhandled exception in the cat code. 6.3(3) is very very old, so chances are that it's been fixed by now. 6.4(21) is the latest in the 6.3/6.4 train, so you may want to consider upgrading to that version.
Also, if you can post a show crashdump 1 as well as a show ver, I can try to decode it to see if it matches a known bug.
HTH,
Bobby
*Please rate helpful posts.