Upload Graphic problem

Hi,

first of all I really love this plugin and I would like to use it at its best.

But I have a problem uploading my personal image.

I tried .JPG, .PNG, .GIF, but no one appeared. I tried savin the images without background and still no response.

Are there some rules about the upload? Like size, file, etc.?

Thanks in advance

http://wordpress.org/extend/plugins/holiday-message/