LrC V 12.5 will not export to Photoshop V 24.7.0

The problem started when I tried the Beta PS with contextual fill.  LR seemed to export, but PS Beta did not open the files.  I have since uninstalled PS Beta (I don't intend to use contextual fill) but cannot get LrC to recognise PS 24.7.0, even though it is installed on my hard drive and was working fine before  I tried the Beta version of PS.  The external editor in LrC Preferences is greyed out.