When I launch the installer and aggree to the terms and conditions, an error message pops up after which the window closes.
Thank you for reporting @hychakt. We’ll get a fix out for this soon.
For what it’s worth based on the panic you received it seems likely the issue here is that you already have state tool installed at the latest version, is that possible? In this case you do not need to run the installer again.
If that’s not the case and you still need to install the state tool, then you could try running the powershell installer instead:
powershell -Command "& $([scriptblock]::Create((New-Object Net.WebClient).DownloadString('https://platform.activestate.com/dl/cli/install.ps1')))"
Note: run the above from cmd.exe.