When upgrading, you need to remember that the Bundle installs routers2 using non-standard paths.
If you are upgrading using 2.15 or earlier, you will need to remember
1) The cgi-bin and docroot are C:\mrtg\wwwroot
2) Your MRTG directory is C:\mrtg\mrtg\bin
3) You will need to rename the newly installed routers2.cgi to index.cgi in the C:\mrtg\wwwroot directory.
If you are using 2.16beta3 or later, then these should automatically detect the Bundle, and will set the defaults appropriately and even rename the routers2.cgi script at the end.
UNIX Systems, ITSS, University of Auckland, NZ
Woe unto them that rise up early in the morning... -- Isaiah 5:11