Running msiexec with PowerShell
It happens because the arguments contain spaces (for example, "C:\Program Files\Mathcad\Mathcad Prime 1.0"). In such cases you must escape the quotes around the arguments.
The escape character in PowerShell is the grave-accent(`).
So the command should look something like this:
msiexec.exe /qb /I "C:\myInstaller.msi" INSTALLLOCATION=`"C:\Program Files\installFolder`" ALT_DOC_DIR=`"C:\Program Files\otherFolder`"