I've had trouble installing material sets on English systems.
This makes me think that it's something to do with the material installer being non-unicode.
Maybe it's the material.inf that's causing the problems. Dunno, it's a crap system anyway :l

(If you'd like to try the English mti.exe, it's available here
http://www.mediafire.com/?tohzp9blat6z4d3 it goes in the main program folder)
Basically you've got two options:
1) Manually install/copy "CSPAINT_ALL\Material\Settings\Material\" to "My Documents\CELSYS\CLIPStudioPaintVer1_0_0\Settings\Material\".
Launch CLIP Studio and it'll update your material database and add all the new files to the root "Mats" folder.

Result: None of the new files will be in categories, you'll have to manually sort/drag them.
OR
2) Delete/replace your English Material database folder ("My Documents\CELSYS\CLIPStudioPaintVer1_0_0\Material")
with the Japanese Material database folder (download it here
http://www.mediafire.com/?8ad7frfq6b6bc11)
Delete all your materials ("My Documents\CELSYS\CLIPStudioPaintVer1_0_0\Settings\Material")
Launch CLIP Studio and it will restore the default (Japanese) materials. Close CLIP.
Manually install/copy "CSPAINT_ALL\Material\Settings\Material\" to "My Documents\CELSYS\CLIPStudioPaintVer1_0_0\Settings\Material\"
Launch CLIP Studio again and it will update your material database and add all the new materials into the correct categories.

Result: Correctly organised but it's all in Japanese
I'm not sure which material installation guide you're following and I don't know if you're using OSX or WIN.
The directions given here are for Windows 7 based on installing the material set CSPAINT_ALL.zip
Also, gief me ur Qumarion