zBrush: Color to Texture not possible?

I've been using zBrush successfully, to make sculpties and paint textures on them using the zProject brush and all has been going fine.
Until today, when for some reason, the Color-to-Texture option is not available. It's greyed out and I can't press it. I've followed the same procedure for painting on my sculpties as I have been following.
I restarted zBrush. I restarted my computer. The Color-to-Texture option is still unavailable. I'm stumped! Any help?

EDIT: Color-to-Texture works for sculpties created from scratch and textured with zProject, but it isn't working for tools I saved and dragged back out. And it USED TO.

If you installed a plugin between then and now it's likely to be the cause. The program doesn't take an awful lot to make it have these weird glitches, but a fresh install usually does the trick when all else fails.

Try to reinit, also make sure that colorize is on and that you didn't discard UVs.

Sometimes if you accidently clicked make polymesh3D twice it screws it up bad.