Transparent background showing up black

It has been awhile but I think you have to set your form to Allow Tranparencies

this.AllowTransparency = true;
or
YourForm.AllowTransparency = true;

that would get rid of the black

I had the same issue but I had just a Panel which should've been transparent so I could see everything underneath it.

The problem was with DoubleBuffered property, it should be set to false.

this.DoubleBuffered = false;

No blackness anymore.