Intermittent build issues

I occasionally see failures in unit tests when NUnit's internal communications fail, which then go away when I retry the build. If you see them, just re-try

One looks like this

System.Runtime.Serialization.SerializationException : The object with ID 2 implements the IObjectReference interface for which all dependencies cannot be resolved. The likely cause is two instances of IObjectReference that have a mutual dependency on each other.
--SerializationException
Server stack trace: 
  at System.Runtime.Serialization.ObjectManager.GetCompletionInfo (System.Runtime.Serialization.FixupHolder fixup, System.Runtime.Serialization.ObjectHolder& holder, System.Object& member, System.Boolean bThrowIfMissing) [0x000ae] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.ObjectManager.CompleteObject (System.Runtime.Serialization.ObjectHolder holder, System.Boolean bObjectFullyComplete) [0x00134] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.ObjectManager.DoFixups () [0x000f1] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize (System.Runtime.Remoting.Messaging.HeaderHandler handler, System.Runtime.Serialization.Formatters.Binary.__BinaryParser serParser, System.Boolean fCheck, System.Boolean isCrossAppDomain, System.Runtime.Remoting.Messaging.IMethodCallMessage methodCallMessage) [0x00077] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler, System.Boolean fCheck, System.Boolean isCrossAppDomain, System.Runtime.Remoting.Messaging.IMethodCallMessage methodCallMessage) [0x000a2] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler, System.Boolean fCheck, System.Runtime.Remoting.Messaging.IMethodCallMessage methodCallMessage) [0x00000] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler, System.Boolean fCheck) [0x00000] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler) [0x00000] in <9689214c1e4645be91df75196bac3cbb>:0 
  at System.Runtime.Remoting.Channels.BinaryServerFormatterSink.ProcessMessage (System.Runtime.Remoting.Channels.IServerChannelSinkStack sinkStack, System.Runtime.Remoting.Messaging.IMessage requestMsg, System.Runtime.Remoting.Channels.ITransportHeaders requestHeaders, System.IO.Stream requestStream, System.Runtime.Remoting.Messaging.IMessage& responseMsg, System.Runtime.Remoting.Channels.ITransportHeaders& responseHeaders, System.IO.Stream& responseStream) [0x0009d] in <7a008740b57d43ebbd138a12134e901a>:0 
Exception rethrown at [0]: 
  at (wrapper managed-to-native) System.Object.__icall_wrapper_mono_remoting_wrapper(intptr,intptr)
  at (wrapper remoting-invoke) NUnit.Engine.Agents.RemoteTestAgent.Run(NUnit.Engine.ITestEventListener,NUnit.Engine.TestFilter)
  at NUnit.Engine.Runners.ProcessRunner.RunTests (NUnit.Engine.ITestEventListener listener, NUnit.Engine.TestFilter filter) [0x00025] in <a3ad5449913a4202999529a949a30f07>:0 

Another looks like

NUnit.Engine.NUnitEngineUnloadException : Multiple exceptions encountered. Retrieve AggregatedExceptions property for more information
  ----> System.Runtime.Remoting.RemotingException : Tcp transport error.
  ----> System.Runtime.Remoting.RemotingException : Tcp transport error.
  ----> System.Runtime.Remoting.RemotingException : Connection closed
  ----> System.Runtime.Remoting.RemotingException : Connection closed
Fake.Testing.Common+FailedTestsException: NUnit test failed (251).
   at Fake.DotNet.Testing.NUnit3.NUnit3(FSharpFunc`2 setParams, IEnumerable`1 assemblies) in C:\proj\FAKE\src\app\Fake.DotNet.Testing.NUnit\NUnit3.fs:line 338
   at Targets.f@51-8(TargetParameter _arg10)