it says there's a problem with the icon size and refuses to load.

I'm using the same version as the one I've uploaded, so if there an icon size problem, I dont know from where the problem come from, and friends used it without any problems. Are you using bob logistics ?

Check your Factorio version? There is something about icon size in 0.15.7 patch note: https://forums.factorio.com/viewtopic.php?f=3&t=46452 .
It might be related.

I have all of the up-to-date Bob's Mods.

This is the error I'm getting:

"Failed to load mods: The given sprite position (left_top = 288x0) is completely outside the actual sprite image (size=256x128). Sprite name: add-loader-u15/graphics/entity/loader/extremely-fast-loader-structure.png

Mods to be disabled:
add-loader-u15"

This is what breith was referring to, from the patch notes:

Icons are now required to have correct size (which can be overridden by icon_size property). (45700)

32x32px for entity, fluid, item, item-group, recipe, technology, virtual-signal

128x128px for achievement, tutorial

If icon path references base mod, technology icon is expected to be 128x128px and item-group icon 64x64px.

In near future, we may remove default sizes and require icon_size to be always specified.