error on uploading new build created using phonegap.

I am currently uploading new build but that shows below error.

"Missing required icon file. The bundle does not contain an app icon for iPhone / iPod Touch of exactly '57x57' pixels, in .png format for iOS versions < 7.0."

I have added below line in my config.xml file and I am sure files are linked correctly.

<icon src="icon.png" gap:platform="ios" width="57" height="57"/>

  <icon src="icon-57.png" gap:platform="ios" width="57" height="57"/>

Please let me know how to resolve that.