Here is the blender file: https://drive.google.com/folderview?id=0B4izbazXuAGMfjhoNjZmcFBBczdIZmhqVmhlUzFTU3VIaG9nREVScnFQVVAtMmxrczQxNVU&usp=sharing
Were the materials there before but now are gone? Have you recently changed the render engine from Cycles to Blender Internal or vice-versa?
I did change the engine but it doesn’t seem to matter, the material slots don’t appear in either of them
I wouldn’t know what happened, but you can repair it creating a new empty file, then importing all your stuff on it.
strange
if u open it up with no load UI you can see the materials list and nodes set up in cycles!
by the way do a save as and set compress
files will be way smaller and less sluggish too !
happy cl
thing I found the thing
look in your material search field for mat
it has letter Z in it
so remove it and it should work fine
happy cl