This probably won't get accepted unless you remove the black border. I looked at your other pieces and I understand you are using Paint, but you should use another free program like GraphicsGale that supports transparency to remove that border!
Here's how to do it in GraphicsGale, step by step:
1) Create a new 64x64 pixel, 24 bit (full color) piece.
2) Copy-Paste the sprite from Paint to GraphicsGale. Right click to deselect.
3) In the top menu, click Image -> Add Alpha Channel.
4) Select the background color with the wand tool, and press Delete on your keyboard.
4a) To make sure you have deleted all the background, change the editor-only Background Color in File -> Properties.
5) File -> Save As... (save as a lossless PNG file, and enable the option "With alpha channel").
The other thing that might be stopping this getting accepted is the 42 colors. Some people here like pixel art that uses as few colors as possible, but I did check the piece and it seems to be 42 legitimate colors, not a lossy compression error. Try looking at resources like DB's 16 color palette, which will help a lot in understanding limited color usage. =)
All your wees look great (especially your dwarf!).