I use MameWah-v1.62b9 so my configuration is a little different than your but should basically be the same settings. Anyway, here are the differences which I have from you:
1) My N64 games have extension ZIP so I start them using ZIP rather than Z64. Double-check your rom files have "Z64" extensions rather than "ZIP" files ..... obvious I know, but worth double-checking the obvious sometimes.
2) I do NOT have quotes around the [rompath]\[name].[romext] stuff
3) I am also using the Project64-1.6 command line wrapper from the CPViewer site.
Are you using this wrapper to try to start your games?
Wrappers are located here:
http://www.emuchrist.org/cpviewer/commandlinewrappers.htm