length and size of audio tracks

Hi,

I seem to be having problems playing single tracks that are 60 mins long.

e.g Created a playlist with one audio track of length 60mins.
Added playlist to calendar and waited for playback to start.
Airtime goes on air as expected but there is no audio from feed. Current playing song shows as 'airtime : offline'. Sometimes it starts with audio but stops after a few minutes.

There is no problem when playing shorter tracks.

Any advice would be much appreciated.