Running on Umbraco 7.5.4 with Courier 3.0.2, it happened out of a sudden that courier doesn't work anymore on a live environment. It was working all this while for a few weeks before this occurs.

We have a staging and production environment (both load balanced), right clicking on a content / media node and selecting Courier pops up the below error. The same error are showing in the logs as well. Any idea what's going on?

Urgently need a fix as the client can't use courier at all and they've paid for the licence.

2017-03-15 14:25:30,753 [56] ERROR Umbraco.Courier.Core.BackgroundTaskRunner - [Thread 56] An error occurred consuming task

System.Web.Services.Protocols.SoapException: Server was unable to process request. ---> Transaction not connected, or was disconnected
 at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
 at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
 at Umbraco.Courier.RepositoryProviders.CourierWebserviceRepositoryProvider.CloseSession(String sessionKey)
 at Umbraco.Courier.RepositoryProviders.CourierWebserviceRepositoryProvider.Dispose(Boolean disposing)
 at Umbraco.Courier.RepositoryProviders.CourierWebserviceRepositoryProvider.Dispose()
 at Umbraco.Courier.Core.Repository.Dispose(Boolean disposing)
 at Umbraco.Courier.Core.Repository.Dispose()
 at Umbraco.Courier.Core.BackgroundTaskRunner`1.ConsumeTaskInternal(T task)