paint.net help

[Metallica1983]

for those of you who use paint.net i need ur help i just made my first sig and i need help uploading it to the forum everytime i try it says invalid file can anyone tell me wut im doing wrong or wut im not doing

[Riku-Nara]

uploading a sig?
ummmm.
well, i just upload mine in imageshack, then paste the image code in my sig box.
( speaking of sigs, i'm supposed to be making you one, aren't i?)

[Metallica1983]

ummm yes ive been waiting