are you using old texture packs? and i think it's 16x16 packs only.

To make a texture pack, make a zip file that contains the files you wish to replace, then place that zip file in the texture pack folder. There’s a handy button ingame to open that folder immediately.

If you place a “pack.png” file in the root of the zip file, it’ll show up as a preview icon. Please make sure it’s square, and of an even 2^x size. For example, 128x128 pixels.
If you place a “pack.txt” file in the root of the zip file, the first two lines will show up as a description for the texture pack.