Run your command, but add a
Shell '%COMSPEC% /c Net Use > c:\mapped.txt'
to the beginning of it - you may be surprised by what you find in the file.

I would NOT use UNCs for installations - if you change the server or share, the program may have problems checking for updates and uninstall. I always map a drive during installations, and use a consistent drive letter, and have never had such issues since doing so.

Actually I am a Rocket Scientist! \:D