Playback Stops Working

[DavidF46]

As a newbie, can someone help me with this problem. Having worked on it a particular Notion 4 file and successfully used the playback facility, when I subsequently reopened it, the playback function wouldn't work although individual notes sound when they are highlighted.Other files opened in the same session playback correctly. Restarting Notion 4 and rebooting the computer made no difference. I did have success by creating a new file, setting up the same instruments and copying the staves across, but after closing the file and reopening it, playback wouldn't work again.

Are there known factors that can cause this problem and is there a solution?

(Win 7 x64, Notion 4, Motu Audio Express)

[GaryExo]

Is it possible that some of the data saved in the original file has become corrupted? By copying said data into a new file you would still be using something corrupted in the new file therefore the problem would persist.