If you are having an issue uploading .png files for Emote and Sub badges. This guide will help you to check and fix the pixel size.

This is the content of the folder you have downloaded. The red box indicate the size for each file (28x28, 56x56, 112x112).

Now to check the pixel size of each picture. (Check Picture Below)
    1. Find and click the Resize button. The Resize and Skew menu will pop-out.
    2. Click Pixels option as seen on picture below.
    3. The numbers indicated on blue box is the size of the current picture. As you can see it's different from each other 118x112. The         size is wrong and cannot be uploaded. (Requirements can be seen at the end). 

Now to change the size. Follow the steps below, so it can be uploaded and don't get error for Twitch.
    1. Make sure you are on Pixels to edit.
    2. Change the size of pixel from ( old 118x112) to ( new 112x112)
    3. Make sure that "Maintain aspect ratio" is unchecked or not tick □. So every time you change, It will not be lock and change             both horizontal and vertical.
    4. Click okay then save file. Then you can now upload this emotes/subs to Twitch. 

    Make sure you keep a copy of each picture for backup. Just right click the file click copy then paste on new folder. 
Twitch Pixel Size Requirements:
*Sub Emote
    1. Twitch emotes must be uploaded as PNG and should have a transparent background. 
    2. They are available in three different sizes, each single PNG file has different size. They must follow this size to be uploaded:             28x28, 56x56 and 112x112.
    3. The individual files shouldn’t be larger than 25 kb.
*Sub Badges
    1. Badges must be uploaded in three different size: 18x18 px, 36x36 px, 72x72 px
    2. The graphics must be uploaded as transparent PNG's.
    3. The file size should not be larger than 25kb.
    4. The graphics must comply with the Community Guidelines and Terms of Service.
    5. The graphics shouldn’t be copied / stolen and/or violate copyright.