Ok let's see here...
Using the fat32 guide linked in my signature, it will teach you how to make your 4.37gb .iso files into smaller .wfbs files for a fat32 system to read.
I would install hermes 222/223 from my signature and use a version of a USB loader that loads on 222 and not 249 (if for no other reason, then to eliminate possibilities, i.e. trouble shooting) and those can be found in the guides for that loader. CFG is in my signature, and the fat32 guide has download links for 222 compatible versions of some loaders. Give them a try and see what happens. If nothing else, it will give us more information.
Also, run a syscheck and post the results.