title: Xamarin.iOS build error System.IO.FileNotFoundException
body: <p>I get this error when I try to build using a distribution provisioning profile </p>
  
  <pre><code>Error       System.IO.FileNotFoundException: /Users/xxx/Library/Caches/Xamarin/mtbs/builds/iOSClient/f4287e1ce437e3e2197bfddb3a942d82/obj/iPhone/Ad-Hoc/optimized/Default-736h@3x.png does not exist
  File name: '/Users/xxx/Library/Caches/Xamarin/mtbs/builds/iOSClient/f4287e1ce437e3e2197bfddb3a942d82/obj/iPhone/Ad-Hoc/optimized/Default-736h@3x.png'
    at System.IO.File.Copy (System.String sourceFileName, System.String destFileName, System.Boolean overwrite) [0x001bd] in /private/tmp/source-mono-4.6.0/bockbuild-mono-4.6.0-branch/profiles/mono-mac-xamarin/build-root/mono-x86/mcs/class/corlib/System.IO/File.cs:112 
    at Xamarin.MacDev.Tasks.SmartCopyTaskBase.CopyFile (System.String source, System.String target, System.String targetItemSpec) [0x0002d] in &lt;4ed71c0d8bd847c3bc4130be1482dce1&gt;:0 
    at Xamarin.MacDev.Tasks.SmartCopyTaskBase.Execute () [0x00116] in &lt;4ed71c0d8bd847c3bc4130be1482dce1&gt;:0    iOSClient           
  </code></pre>
  
  <p>any ideas what the cause might be?</p>