1) Are you using the latest version of MAME?
2) Do you have an up-to-date MAME.DAT file in your Mame directory?
If not, run the following from the command line in your MAME directory:
-mame -listxml|xml2info > mame.dat
3) I would change List Generation Method to "2" for Rom Folder Vs DAT File
4) If these are right, then refresh your games list within MameWah by hitting 2-arrow down-1-1 (assumes you are displaying your Main List)
Hope this helps