Fpcupdeluxe uses online sources to install packages.
However, these sources are fast changing and moving all the time.
Now it seems that these vtv-sources are no longer updated due to the fact that they are included (again) with Lazarus !
So, just install the latest vtv by installing the vtv that comes with Lazarus.
This vtv is also used by the very nice OPM !
See:
\lazarus\components\virtualtreeview\virtualtreeview_package.lpk
\lazarus\components\onlinepackagemanager\onlinepackagemanager.lpk
I will update fpcupdeluxe to use these packages !
See next release (not released yet, but will release in a few days).
EDIT.
I have uploaded a pre-release.
Feel free to try:
https://github.com/newpascal/fpcupdeluxe/releases/tag/v1.6.1h