Put some custom mats in the the Zstartup\Materials folder. Everything worked great for about 3 weeks. Then all of a sudden, my load materials button is greyed out. Tried deleting out the mats from the folder but no luck. How do i make this stop?
It doesn’t look like you have a material actually selected at the moment, perhaps because you have a selected tool that doesn’t use material. If no material is selected, the Load button will not be functional because loading replaces whatever the currently selected material is.
pull a few materials out of the startup>materials folder and see if that helps. Maybe you recently added some other files to one of the other startup folders for alphas or textures and that might have topped off your pre-load memory allowance?
Sven
Thanks for the replies guys. Unfortunately, I tried both of those things before posting and no dice 
Aurick, you can see on the mesh to the left that the it had the currently selected material on it in the 2nd material dropdown screengrab. I had a different material selected for the other material menu up top but comped the two images together just to show it was greyed out in both menus. Is there a place to change my pre-load memory balance? I have many gigs of ram to spare.
Is an old good tip dont modify the native zfolders except for the zplugs>zscript file.
Is better to create other folder in a different root than Z3.
Andreseloy
I could reproduce this but the moment I removed the extra materials I got the Load button back (after a ZBrush restart). Have you added Alphas or Textures to the startup folders too? If you have then I suggest you clear those completely (and the Materials) temporarily.
Actually, the ZStartup folder is there for you to modify. That’s why it has the empty material, alpha and texture folders – anything that you put into those folders will be loaded automatically when ZBrush launches.
The only folder in ZBrush that’s “off limits” is the ZData folder and its contents. That folder should never be touched.
Hi
I recently had this problem too and I cleaned out all the materials in the startup>materials folder and the button came back.
Reloaded the matcaps I had stored and the button greyed out.
Anyway after fiddling for a while it seemed to be a max limit of 25 materials (all matcap) was what was triggering it…put 26 in and it switches to grey.
I havent tried a combo of matcap and modified saved materials all in the startup file totalling 25 or more yet, anyone know why this happens? (ie is it known that you can only have a max of 25 matcaps?)
It’s total material count. Each of the ZStartup folders has a maximum number of items that can be put in. This has to do with the size of the window on a display set to the lowest supported resolution. If more items were allowed, the window would become too big for those smaller resolution displays.
Additionally, there’s a memory requirement to think about. Everything in the ZStartup gets loaded into memory when you launch ZBrush. MatCaps can especially get to take up a lot of RAM due to their light maps. So the more (of anything) that you put in the ZStartup folders, the more ZBrush performance will suffer. The limits are there to help protect you from yourself. 
same here… adding the RS material pack to startup mat folder disables the load button…
Thanks Aurick, its good that zbrush watches out for us like that
And yes, the RS Pack is what triggered mine too.
No, you cannot remove any of the default startup materials.