the one pc - that I had manually upgraded to KTS 20 - completed successfully the upgrade
the 2 other pcs - that I had uninstalled KTS - completed successfully the upgrade
I re-installed KTS 20 and are working fine
so, as far as I know, KTS 18 has a problem with 1903
Also, there should be an auto-upgrade to latest version for KTS
THANKS the original poster for the solution