I'm guessing that your system has both IIS and apache installed. The install.pl script guessed you want to install routers2 in the IIS directory -- but you have the MRTG Bundle and so it guessed wrong. Run the install, and tell it the correct directory to install into, and where all the other files should be located.
You can copy the routers2.cgi over the top of your Bundle install index.cgi, but this may not fully work if it is pointing to a different set of directories.
UNIX Systems, ITSS, University of Auckland, NZ
Woe unto them that rise up early in the morning... -- Isaiah 5:11