I've worked out the sequence that caused the problem & the fix.
1) Tried to install from non-admin user and had to cancel.
2) Installed S/W from admin user & using without problems.
3) Problem manifests itself that when rt clicking drives on non-admin user windows installer starts, msg must be admin user, clicking OK resulted in a STOP 0s 50.
1) Changed non-admin user to admin user, rt clicked drive letter, windows installer started and did some configuration without reinstalling software.
2) Changed user back to non-admin & now get rt pop-up menu when rt clicking drive.
MS only know why rt clicking drive letter resulted in windows installer loading.
Lack of application and system testing of how windows installer cancel is handled on non-admin user?