title: Xamarin build error Exception while loading assemblies: System.IO.FileNotFoundException
body: <p>always i try to Build my Xamarin app i get this error. And i dont know why.
  I use the System.Security.dll of .Net Framework 4 and i though this should work.
  Thanks.</p>
  
  <blockquote>
    <p>C:\Program Files
    (x86)\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(2,2):
    Error: Exception while loading assemblies:
    System.IO.FileNotFoundException: Could not load assembly
    'System.Security, Version=4.0.0.0, Culture=neutral,
    PublicKeyToken=b03f5f7f11d50a3a'. Perhaps it doesn't exist in the Mono
    for Android profile?</p>
    
    <p>Dateiname: 'System.Security.dll'</p>
    
    <p>bei
    Xamarin.Android.Tuner.DirectoryAssemblyResolver.Resolve(AssemblyNameReference
    reference, ReaderParameters parameters)</p>
    
    <p>bei
    Xamarin.Android.Tasks.ResolveAssemblies.AddAssemblyReferences(List`1
    assemblies, AssemblyDefinition assembly)</p>
    
    <p>bei
    Xamarin.Android.Tasks.ResolveAssemblies.AddAssemblyReferences(List`1
    assemblies, AssemblyDefinition assembly)</p>
    
    <p>bei Xamarin.Android.Tasks.ResolveAssemblies.Execute()
    (TaskManager2)</p>
  </blockquote>