This started happening to my nsmbw hack years ago and I never got to the bottom of it. Either i had put too much stuff in and/or the iso/partition/reggie became corrupt. Funnily enough a few weeks ago I tried it again with reggie next and it seems to be fixed. However...
1st thing to check is that you have the arc file for the firebars in your partition. Could be missing/deleted/moved....
You'll need to find the object list to find out the name of the file but if it is there, make sure your reggies upto date and maybe try redownloading it to fix any corrupt files there.