Thanks Saby

I again uninstalled PS23U + Content, cleaned the Registry and re-downloaded/Installed the PS23U package.  Same issue, the .m2ts (AVCHD Video) files have no audio when played in the Library or the Timeline of PS23.  Other file types play audio OK on the same Track.  The AVCHD Video files play OK in PS22.

A ticket has been raised with Corel Technical support.

Chris C