shibboleth-sp-3.0.4.2-win64 install issue on Server 2016

[Rod Widdowson]

> Msiexec returns the error “This installation package could not be opened. Verify that the package exists and that you can access it, 
> or contact the application vendor to verify that this is a valid Windows Installer package.”. 

As you diagnosed this is environmental and nothing to do with the installer.  I'd advise you to check your Global security policy for anomalies, third party security products can also get in the way..  I'd also suggest checking that you are correctly elevated and ensure that the "this has been downloaded ADS" is stripped (its on the properties page).

In any case your go-to tool for situations like this is Procmon, downloaded it from the MS website.

/R