Randomly Corrupted jpegs

Macmini with 4G RAM, using CS4

After editing a jpeg file and saving it on the internal hard drive we can go back and read it OK. We copy the edited jpeg to an external drive via firewire 800. This has been our process for >1 yr. (note that the firewire based drive was moved from another mac in the house to this one roughly about the same time we started seeing the corruption - don't know if that is coincidence or not)

In the last few months we have started to see random jpeg corruption on both the internal and external drives with pictures taken over the last few months. Sometimes a file is corrupted on the external but not internal drive and sometimes it is the other way around.

Attempting to open the file in photoshop results in a "file corrupted, may be truncated" type message. Trying multiple other programs to open the file results in the same visual effect - portions of the picture are missing and replaced by coloured jagged lines.

Any ideas on what is going on. I have seen several posts on multiple sites (windows and mac) with lots of speculation but no answers.

I had a similar issue a while back... although it was only ever the images on my external HD. I used Disk Utility to repair the drive and haven't had a problem since - the corrupt files stayed corrupt though, I just haven't had any new ones go bad.

thanks for the info. I used the disk utility that came with Snow Leopard tonight and it found that there were several disk errors but no files were recovered. still trying to figure out why the transfer corrupted some destination files and some source files but not necessarily the same ones