you need to wait for a Nintendont fix, or use a beta version of USBLoaderGX which is not using arguments.
there are two booting method to launch nintendont:
Normal (slower, old method)
argument (faster, new method)
since Nintendont r304, the argument method is broken, so I made a version of USBLoaderGX which use the old (normal) method only.
Note that this should be a temporary solution until nintendont fix the issue with loaders booting using argument method.
http://www.mediafire.com/download/jau551jer8n95yb/USBLoaderGX_1244mod01.7z
just replace the boot.dol in your usbloader_gx folder with the one from the link.
I didn't get a lot of report about this beta version. I'll be happy to know if it fix your issue.
Saying to use CFG of Wiiflow shouldn't fix the issue, unless they are working with the old method only.
I think the loaders are not updated anymore, unless you use abdallahTerro mods.
but, let the user choose the loader he prefer.