Read up on FILL LEFT and FILL RIGHT.
I'm looking for a complete answer, not a suggestion.
I searched the internet prior to asking here, found nothing
I think that what Harm was recommending was adding the appropriate Fill Left, or Fill Right Effect to get your 1-channel Audio Stream (in a 2-channel Clip), into both channels. Effects>Audio>Fill Left or Fill Right.
Well that makes sense and it appears to be a very quick fix,
rather than my : Edit Clip In Audition (step step step ) multitrack session (step step step) export as MP3
Thanks to both for the responce.