Web Part Error: No available sandboxed code execution server could be found. Correlation ID: 0bcaaf9f-4c79-1024-50f1-e2b1f1a52387.

Error Details:
[SPUserCodeExecutionPipelineFailedException: No available sandboxed code execution server could be found.]
  at Microsoft.SharePoint.UserCode.SPUserCodeExecutionManager.Execute(Type userCodeWrapperType, SPSite site, SPUserCodeExecutionContext executionContext, SPUserCodeActivationSiteInfo activationSite)
  at Microsoft.SharePoint.UserCode.SPUserCodeExecutionManager.Execute(Type userCodeWrapperType, SPSite site, SPUserCodeExecutionContext executionContext)
  at Microsoft.SharePoint.UserCode.SPUserCodeWebPartRemoteExecutionHelper.<>c__DisplayClassa.b__9()
  at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode)
  at Microsoft.SharePoint.UserCode.SPUserCodeWebPartRemoteExecutionHelper.ExecuteRequestInSandBox(HttpContext context, SPWeb web, SPWebPartManager manager, SPUserCodeWebPart userCodeWebPart)

[SocketException: No connection could be made because the target machine actively refused it 10.250.2.50:32846]
 
 Server stack trace:
  at System.Net.Sockets.Socket.Connect(IPAddress[] addresses, Int32 port)
  at System.Runtime.Remoting.Channels.RemoteConnection.CreateNewSocket(AddressFamily family)
  at System.Runtime.Remoting.Channels.SocketCache.GetSocket(String machinePortAndSid, Boolean openNew)
  at System.Runtime.Remoting.Channels.Tcp.TcpClientTransportSink.SendRequestWithRetry(IMessage msg, ITransportHeaders requestHeaders, Stream requestStream)
  at System.Runtime.Remoting.Channels.Tcp.TcpClientTransportSink.ProcessMessage(IMessage msg, ITransportHeaders requestHeaders, Stream requestStream, ITransportHeaders& responseHeaders, Stream& responseStream)
  at System.Runtime.Remoting.Channels.BinaryClientFormatterSink.SyncProcessMessage(IMessage msg)
 
 Exception rethrown at [0]:
  at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
  at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
  at Microsoft.SharePoint.Administration.ISPUserCodeExecutionHostProxy.Execute(Type userCodeWrapperType, Guid siteCollectionId, SPUserToken userToken, String affinityBucketName, SPUserCodeExecutionContext executionContext)
  at Microsoft.SharePoint.UserCode.SPUserCodeExecutionManager.Execute(Type userCodeWrapperType, SPSite site, SPUserCodeExecutionContext executionContext, SPUserCodeActivationSiteInfo activationSite)