Help! Does anyone here use Papel

[BookCat]

I've started using the freeware Papel, to organise writing projects. It's great, but I want to create my own icon set. I've gathered together a bunch of appropriate icons, on a cat theme, all the correct size, and I think I've adapted the ini file correctly.

Why won't it work?

One of the ready-made themes works, and I just can't see where I've gone wrong. I never was any good at html. This is supposed to be easy, according to the software.
Any help would be much appreciated if someone knows what I'm talking about. I've googled this till I'm blue in the face, but can't find a thing.