Painting terrain problem

I was having the exact same problem. As absurd as it might sound it's gone after reseting unity to the default layout (Window -> Layouts -> Default)

Now I can paint with all the textures again and the brush works normally.

Did you try loading a texture first into the texture boxes?

Read through this page for step by step instructions on how to paint textures onto your terrain...

http://unity3d.com/support/documentation/Components/terrain-Textures.html

I had that Problem too, but after changing every possible option I realized that the slider "Target Strength" was set to 0 so I had no Chance to paint anything.

I had this same problem of not being able to use paint or elevation tools for the terrain editor, and rebooting didn't work. Window, Layouts, Default fixed the bug! Also make sure opacity is 50+ or you might not see the brush working.

I ran into the same problem. Rebooting did the trick once and now it's back to "Texture painting? I can't let you do that Dave..." I'll try to open my project on a different machine with a fresh Unity install, let's see if the bug persists. My version is 4.1.5f1 btw.

Update:

I upgraded my Unity to 4.2.0f4 with no apparent effect. Editing older projects functions without an error, new ones come up with the known issue. After opening my project on a different computer with a fresh Unity install, I got suprised with a completely working project. I'm now copying the fresh install onto my regular working machine, maybe it'll help.

Update 2:

Copying the functioning installation over my faulty one did not result in the desired effect. Im now going to export the projects terrain content to an older, working one

Update 3:

The exported data functions just as wanted. For now im going to paint the Terrain in a different project. After finishing, it will be reimported to my original one. Damn unpractical solution...