Which revision of the loader, I wonder, though? Go into your USB Loader GX Settings, and check the Credits. Should see a revision number for it (and groove to the music while you're at it.)

It also shows your cIOS numbers.
Mine reads: Rev844 IOS 249 (Rev 14).
Looks like they're up to 866
here. As you can see, it is CONSTANTLY updated. If you're on an old revision, get the .dol file (not the wad, as it has warnings attached to it. Don't know why the wad is needed.) Replace the .dol file in the proper loader folder on your SD card (I believe it still needs to be titled boot.dol or whatever, and should be in the apps folder.)
I'm using cIOS rev14 myself as well (which is shown as the IOS 249 rev14 above.) 15 apparently has some issues, and 14 seems to work great.
Made some edits