Parts of my UV do not want to render

Question

So, I've been working on this model, made a decent retopography, but then I noticed while trying to make a Normal-Map on the hands, it was sloppy and didnt' work. So to be quick and out of lazyness I decimated the crucial parts (the Hands and toes of the feet) of my high-res, advanced it a little and then added it to the retopography. (you know, cut off hand of High-Res, Decimate, SubSurf-Mod, Shrinkwrap to Highres, --> apply all, then Ctrl+J to the Retopography, Bridge it to Arm and feet, Symmetrize, finish) looks better in any way.

NOW THE PROBLEM: I unwrapped the model another time, and made the UV-Grid show, so I could reduce the stretching on the UV, but on the Newly made Parts, no UV-Grid shows on the 3D editor, it's just blank..? The UV is in the UV-Editor still.. What causes this? What do I do? Is it just Recalculate Normals?

Answer 1

OK, I found out, because I copied It from another resolution Model, I unusually had a different Material set for this specific parts, so it wouldn't choose the right texture image. I deletet all the materials and made a new one now it works.