Application Icon is not loaderd

Dear Sir,
i am trying lots of time to upload Application Icon , but every time after select the image it shows ” The file logo512x512.png has been uploaded.” but when i try to save changes it shows blank icon . my url is ” http://knowledgetuts.com/wp-admin/options-general.php?page=pw_mobile_app_options&tab=pw-mobile-build-options” so please guide me how can i update my app. icon.

https://ww.wp.xz.cn/plugins/androapp/