RStudio fails to launch after update

I'm running Windows 10, just downloaded and installed R 4.0.0, then RStudio v.1.2.5042.
Standard RStudio installation installs correctly (or seems to) but throws fatal error during configuration as it can't find the installation package 'RStudio_1.1.453_R01.msi'
Error message: "The feature you are trying to use is on a network resource that is unavailable."
RStudio suggests C:\windows\ccmcache\o\ as the path.

I have now tried with the latest preview version too RStudio-1.3.958, no improvement, same errors.
Help welcome, thanks.