Download file from ftp server not work on build release.

I download my file from ftp server my host : ftp://ftp.myhost.com
My code work fine on Unity Editor and PC,MACs but it don’t have connection on Android when i build release.
I show the log on ddms and it have exception :
System.Net.WebException: The remote server name could not be resolved.
It work fine with Android build development.
Please help me.

http://botsitgames.com/unity-engine-ftp-uzerinden-dosya-cekme/