Westsideguy. Thanks for the info. Sounds like this could be the solution. I found the file (using Pathfinder) but have no idea what a zero length file is or how to tell. Tried to delete the file instead, but can't, even though I changed permissions from Root & Wheel. Also tried a new download of 10.3.6 from the Mac site as you did but still no joy. Might have to reload Panther and start again but I really have better things to do with my time!!
Thanks again for the help.