What does this AHT error code mean

Hi, I have been having some problems with my disk, specifically periodic hangs which appear to be a result of disk I/O errors. I have run the Apple Hardware Test and it has given me this cryptic result:

4SNS/1/40000000: TmOP-63.125

I believe this is not a disk error but could anyone tell me what it is? Also does this mean I don't appear to have a disk problem or does the test just finish when it finds an error?

Many thanks, Ben.