Make a copy of the MAT file, change those lines, and see if that works. (Or you could use the original, and just reinstall if you need to.)

If you don't want to do that, contact DAZ tech support. There may be something wrong with this product. Most of us bought the David Bundle, which came with standard-res textures. If there's a problem with the high-res textures, it's possible no one noticed until now.