title: xamarin.android project deployment errors
body: <p>i made a project to try and use admob banner but when i deploy the project on my device (api 21) i get a "there were deployment errors. continue?" massege but when i run it on my emulator(api 23) it works perfectly.
  my target android version and target framework version are both set to api 21</p>
  
  <p>this is what i get in the output window</p>
  
  <p>sorry for the length i wasnt sure how much of it to put</p>
  
  <pre><code>         :Deployment failed
            2&gt;Mono.AndroidTools.InstallFailedException: Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE]
  2&gt;   ב-  Mono.AndroidTools.Internal.AdbOutputParsing.CheckInstallSuccess(String output, String packageName)
  2&gt;   ב-  Mono.AndroidTools.AndroidDevice.&lt;InstallPackage&gt;c__AnonStoreyE.&lt;&gt;m__0(Task`1 t)
  2&gt;   ב-  System.Threading.Tasks.ContinuationTaskFromResultTask`1.InnerInvoke()
  2&gt;   ב-  System.Threading.Tasks.Task.Execute()
  2&gt;The "InstallPackageAssemblies" task failed unexpectedly.
  2&gt;System.AggregateException: One or more errors occurred. ---&gt; Xamarin.AndroidTools.AndroidDeploymentException: InternalError ---&gt; Mono.AndroidTools.InstallFailedException: Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE]
  2&gt;   at Mono.AndroidTools.Internal.AdbOutputParsing.CheckInstallSuccess(String output, String packageName)
  2&gt;   at Mono.AndroidTools.AndroidDevice.&lt;InstallPackage&gt;c__AnonStoreyE.&lt;&gt;m__0(Task`1 t)
  2&gt;   at System.Threading.Tasks.ContinuationTaskFromResultTask`1.InnerInvoke()
  2&gt;   at System.Threading.Tasks.Task.Execute()
  2&gt;   --- End of inner exception stack trace ---
  2&gt;   at Xamarin.AndroidTools.AndroidDeploySession.&lt;RunLoggedAsync&gt;c__async1.MoveNext()
  2&gt;--- End of stack trace from previous location where exception was thrown ---
  2&gt;   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
  2&gt;   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
  2&gt;   at Xamarin.AndroidTools.AndroidDeploySession.&lt;StartAsync&gt;c__async0.MoveNext()
  2&gt;   --- End of inner exception stack trace ---
  2&gt;   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
  2&gt;   at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
  2&gt;   at System.Threading.Tasks.Task.Wait()
  2&gt;   at Xamarin.Android.Tasks.InstallPackageAssemblies.Execute()
  2&gt;   at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
  2&gt;   at Microsoft.Build.BackEnd.TaskBuilder.&lt;ExecuteInstantiatedTask&gt;d__26.MoveNext()
  2&gt;---&gt; (Inner Exception #0) Xamarin.AndroidTools.AndroidDeploymentException: InternalError ---&gt; Mono.AndroidTools.InstallFailedException: Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE]
  2&gt;   at Mono.AndroidTools.Internal.AdbOutputParsing.CheckInstallSuccess(String output, String packageName)
  2&gt;   at Mono.AndroidTools.AndroidDevice.&lt;InstallPackage&gt;c__AnonStoreyE.&lt;&gt;m__0(Task`1 t)
  2&gt;   at System.Threading.Tasks.ContinuationTaskFromResultTask`1.InnerInvoke()
  2&gt;   at System.Threading.Tasks.Task.Execute()
  2&gt;   --- End of inner exception stack trace ---
  2&gt;   at Xamarin.AndroidTools.AndroidDeploySession.&lt;RunLoggedAsync&gt;c__async1.MoveNext()
  2&gt;--- End of stack trace from previous location where exception was thrown ---
  2&gt;   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
  2&gt;   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
  2&gt;   at Xamarin.AndroidTools.AndroidDeploySession.&lt;StartAsync&gt;c__async0.MoveNext()&lt;---
  2&gt;
  2&gt;Build FAILED.
  2&gt;
  ========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========
  ========== Deploy: 0 succeeded, 1 failed, 0 skipped ==========
  </code></pre>