"invalid color depth" etc

I just want to ask a general question about the arbitrary occurrence of these error messages. I export all my graphics the same way, but SOMETIMES it tells me they are invalid, and sometimes it's fine with them. I always index my images, so the color depth should not be a problem. Is there anything else I could possibly be doing wrong or is this some kind of retarded glitch? Either way, it's unbelievable frustrating, especially when it persists across every possible file format, as if it's the image ITSELF and not its color depth or format.

Does ANYONE know what the hell this is caused by?
And just so I'm clear, I am saving this as a 256 color PNG. It is flat, 1 layer. No transparency, though that shouldn't be a problem anyway. There is NO REASON this should not be working.

Even when I try saving it as a 256 color BMP, it still says INVALID COLOR DEPTH.

The insane thing is that if I take another of my charsets, it's uploads fine, but if I copy that working charset and paste THIS one one top of it, and then save it with the same settings, it is no longer compatible. What. The. Fuck.

This program is being such a faggot.

Your sure its 256 color? I always use Irfanview and check to make sure, cause even tho file properties says so. Its not always right.