slight anticipation

[dub]

hi guys,

a strange thing occurred to me yesterday.
I have a complete song done in Ableton Live 4.04 (pc win2000 usb audio 4 soundcard) when i render it to disk as a wav file i can hear that some of the voices are slightly anticipated, while re-listen to the song in Live they sound alright.
this happens only towards the end of the song... latency issue?? don't think so, otherwise i should listen in the song in LIve as well..

any help appreciated

p.s. i've been using Live since 2 years by now..never happened this thing before.