weird... well if you have luck trying Andy's recommendations (and I think you will) it might be a problem any more
but.... if you still want to do it from MP3s (bearing in mind the lower quality as Andy mentioned) - has it happened more than once? I'm thinking jitter while burning....
have a go with WAVs - remembering that audio data is just that - ignore file sizes cos the standard CDA doesn't look at them the same way your OS does
good luck