problems with 7800.rom working (HELP!!)

[problems with 7800.rom working (HELP!!)]

i have downloaded the version of MESS off of this website, as well as the required 7800.rom file. However, every time i click on the 7800 NTSC system, it says that there is a missing file (7800.rom). How do i get the system to recognize that the 7800.rom file is there, or where do i need to put that file so it can recognize it.

 

Thanks!!!