TLMGR reports "location-url C:/TeX/Live/2019/tlpretest ERROR" and stops.

[Taylor, P]

I endavoured to update my TeX Live 2019 pre-test installation for the first time a few moments ago, and having re-rsynch'd I then launched "TeX Live Manager" from Start Menu / Programs / TeX Live 2019 as adminstrator (since it won't launch at all in user mode).  It reported that TLMGR required updating, reported that it had updated and relaunched it, still reported that it required updating, and when I tried "Update all" was told :
location-url    C:/TeX/Live/2019/tlpretes    t
ERROR
Can anyone advise, please ?
Philip Taylor
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