Need help, I can not build app on IPad, but on simulator work fine.

when I build it on IPad, get such error: Error MT2002: Failed to resolve "System.Void MonoTouch.Foundation.NSObject::InitializeHandle(System.IntPtr,System.String)" reference from "monotouch, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065" (MT2002)

Any suggestion would be great.