NANT: nunit3-console.exe requires the --inprocess swtich on one enviroment but not another

Question

Using the following NANT script to execute an NUNIT test assembly (using nunit3-console.exe):

<target name="Test">
     <exec basedir="${nunit.base.dir}"
                   workingdir="${unittest.test}" 
                   program="nunit3-console.exe" 
                   commandline="Test.dll" 
      failonerror="true" />
</target>

works fine on one machine, but on a different machine using the exact same basedir path, workingdir path, and Test.dll assembly, results in the following exception thrown by the nunit console runner (3.4.1):

[exec] System.Exception: Unable to acquire remote process agent
[exec]    at NUnit.Engine.Runners.ProcessRunner.CreateAgentAndRunner()
[exec]    at NUnit.Engine.Runners.ProcessRunner.LoadPackage()
[exec]    at NUnit.Engine.Runners.AbstractTestRunner.Load()
[exec]    at NUnit.Engine.Runners.AggregatingTestRunner.LoadPackage()
[exec]    at NUnit.Engine.Runners.AbstractTestRunner.Load()
[exec]    at NUnit.Engine.Runners.MasterTestRunner.LoadPackage()
[exec]    at NUnit.Engine.TestEngine.GetRunner(TestPackage package)
[exec]    at NUnit.ConsoleRunner.ConsoleRunner.RunTests(TestPackage package

If I use the --inprocess switch it will resolve the immediate issue. However, I need to use the --x86 swtich as well. --inprocess and --x86 are not compatible.

Any suggestions would be greatly appreciated.