I wonder why this could be happening: a previously working file suddenly won't render properly in the preview window, giving errors and a gray image. It started when I unhooked a water shader from the child input of a surface shader, and hooked it back on. Tried another water shader, same result. A reflective shader worked fine, as did the color of that surface shader when checked.
After that things got worse; with the water layer (sphere) off, errors still occurred, naming an object as the culprit (and it hasn't even been populated yet) and every time I delete that object and reopen the file, another object is the culprit.
I'll check some other files, maybe reinstall TG, but if anyone has an idea, it's most welcome. I don't know if this has to do with it being an alpha version (2.4.29.0) though...[attachimg=1][attach=2][attach=1]