When you are starting installation of some package via MSI, and if you ran into error like this:
“Error reading from file _full_path_to_msi_package. Verify that the file exists and that you can access it.”
check that Local System account has read access over containing folder and .msi file itself.
First phase of installation starts under your account, so it will start as expected, but in some moment, one phase is executed via Windows Installer service, which in turn works under Local System account.