Asset UPnP 4.01 install failed - "error 1603"

I purchased Asset UPnP for my WHS 2003 (RipNAS), tried to install it via the add-ins function as described in the manual, but the install process stopped with error message (1)

"A network error occurred while attempting to read from the file C:\Documents and Settings\All Users\Application Data\Microsoft\Windows Home Server\Asset-Install.msi"

After the "OK"-click error message (2) says:
"The selected add-in failed to install. The error code was 1603. Please contact the add-in Author for assistance"

I could not find any forum entries, FAQs or else anywhere dealing with this problem - does anyone have an idea what is going on here and how to proceed?

Remote Desktop connect to the WHS box, open control panel and uninstall the old asset with Programs and Features (if installed)
Create a folder C:\install\ on the WHS box, copy the .msi install there and run it.