One of the first problems I ever ran up against in Windows Vista was a program installation which would halt immediately after I started it with the error “Invalid Drive Letter M:\”. On my machine, the M drive is a mapped network drive which I have set as my “My Documents” location (so my important files are saved on our server which gets backed up nightly).

Apparently, moving your “My Documents” folder to a mapped network drive and Windows Installer 3.1 do not get along. The fix was to temporarily move my My Documents location back to a local drive (i.e. C:\Users\Profile\Documents), install the program and then move the location back to the network.

This change allowed me to install the program with no problems. Of course, this is an annoyance, but it’s something I can live with.