What file format are they?
mp3, wma, ogg, wav, m4a, flac, other?
Have you installed any 3rd-party plugins
Does the length show if you right-click the ml entry and select 'read metadata on selected items'?
Can you upload a sample file to eg. sendspace.com or mediafire.com and post the download link here?
(we'll need a sample file if we're going to be able to reproduce the problem, because as it stands, we can't).