On windows XP system,Originally posted in cdnusers.org by rajpcb
Select Mycomputer, Right mouse button click, go to properties, jump to advanced. Here you can click on environmental variables and set your Allegro_brd2odb under system variables. Allegro should do that automatically when u install by going to Allegro menu File>export>ODB option.
My variable now reads Allegro_brd2odb = C:\Valor\ODB++Inside
Try this and this should help you.