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?