installing studio 2021 SR1

I just purchased sdl studio 2021 sr1 for use on 2 computers simultaneously.

After downloading the exe file and opening it, the installation stops with error message 1603.

I have previously been using studio 2019 sr2, but according to the release notes for 2021 it is not necessary to uninstall 2019 before installing 2021.

Please advise.