Unable to mount boot partition

I have compiled a custom environment using Yocto. I have most everything working now, but I've hit one major problem. The system boots fine, but after it does, I can't mount the boot partition. When I try, I get the following error:

root@beaglebone:/# mount /dev/mmcblk0p1 /boot
FAT-fs (mmcblk0p1): codepage cp437 not found
FAT-fs (mmcblk0p1): codepage cp437 not found
FAT-fs (mmcblk0p1): codepage cp437 not found
mount: mounting /dev/mmcblk0p1 on /boot failed: Invalid argument

I've googled as best I can and I made some changes in the keel that I thought might fix this:

I changed File Systems > Native Language Support > Codepage 437 and NLS ISO 8859-1 from "M" to "*". So as best I understand it, support for codepage 437 should be built in to the keel.

I don't know how to be 100% sure that my build process (yocto) is really working, and that this change made it in there.

Is there a way to query the keel for active codepages?

What could be going wrong?

I don't know if it's relevant, but /proc/filesystems lists vfat as an option:

ext3
ext2
ext4
vfat
msdos

Also, I should mention the partition is fine. If I boot debian from an SD card I can mount that partition without difficulty.

One last thing that may be important. I'm using busybox, so the mount command I'm using isn't the normal mount, but is actually busybox.