title: MSBuild exec task, exit code empty
body: <p>I have the following exec task, performing checkin of assemblyinfo.cs files. I'm trying to return the exit code, but for some reason it is always empty. </p>
  
  <pre><code>&lt;!--Checkin if all succeeded--&gt;
  &lt;Exec Condition=" '$(LocalCompilationSuccess)' != 'Failed' and '$(LocalTestSuccess)' != 'Failed' " ContinueOnError="True"
                Command='&amp;quot;$(TfCommand)&amp;quot; checkin /recursive /comment:"$(NoCICheckInComment) $(BuildDefinitionName): build succeeded, checkin changes." /override:"TeamBuild $(BuildDefinitionName)" $/SomeProject/Trnk' WorkingDirectory="$(SolutionRoot)"  &gt;
    &lt;Output TaskParameter="ExitCode" PropertyName="ErrorCode"/&gt;
  &lt;/Exec&gt;
  </code></pre>
  
  <p>I've tried to read the exit code in 2 ways: </p>
  
  <pre><code>'%(ErrorCode.Identity)'
  '$(ErrorCode)'
  </code></pre>
  
  <p>Both are empty. Any suggestions?</p>