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.