Access Denied - PSEXEC Called from TFS

I am implementing a continuous integration scenario for a SharePoint deployment. After all the features have been built on the build server, I try to deploy the new features to the test server by running STSADM commands through PSEXEC.

When I run my script from whatever computer I go to, it works fine. When I add exec command to my team build project

 <Target Name="AfterDropBuild">
       <Exec Command="c:\progra~1\pstools\psexec.exe \\testserver -u mydomain\mydomainuser -p mypassword \\BuildServer\CurrentBuild\DeploymentFiles\Deploy.cmd" />
  </Target>

      

        
        
        
      

    

The build partially fails and I get an error that is denied in my build logs:

Task "Exec"
  Command:
  "c:\progra~1\pstools\psexec.exe \\testserver -u mydomain\mydomainuser -p mypassword \\BuildServer\CurrentBuild\DeploymentFiles\Deploy.cmd"
  Access is denied.

      

        
        
        
      

    

I added the TFS service account as a local administrator on both the build server and the test server.

Any ideas on why this might work on any box where I am an interactive user, but not when psexec is run from a build agent?