NGUI black border on png and targa

Hi, im new to nGUI, i make a new atlas with some png files but when the bkg color change i see them with a black outline and i dont know how to remove this artifact. The png icon is completely white and i use the Flaming Pear plugins (Solidify B) to fill the icon with a solid color and i create also an alpha channel. I export the image with "save for web" in png and in tga format but i have the same issue with the two different image format. You can see the screenshot below and i attach the psd file of the icon, have some ideas?[1]