This can happen when the environment variables are missing an entry for Powershell. $env:path must include C:WINDOWSSystem32WindowsPowerShellv1.0;. As mentioned in the comments, the installer likely added this entry to your path after not finding it on the first run of the installer.
To anyone else reading this in the future, try running the installer a second time. If you encounter the error again, check your environment variables and manually add the entry for Powershell.