Error MT1009: Could not copy the assembly
This issue has been resolved in recent versions of Xamarin.iOS. However, if the issue occurs on the latest version of the software, please file a new bug with your full versioning information and full build log output.
As described in our Release Notes, this is a known issue in Xamarin.iOS 7.2.6. This issue is due to file permissions needing higher privileges when Xamarin.iOS is installed with a different user account then the developer's main account.
To workaround the issue, please open the Terminal.app on the Mac workstation and run the following command:
sudo chmod 0644 /Developer/MonoTouch/usr/lib/mono/2.1/monotouch.dll.mdb