BizTalk Error

I have come across yet another error in BizTalk, I'll be looking into this one and posting a solution as soon as I find it:

Microsoft.XLANGs.Core.XlangSoapException: An error occurred while processing the message, refer to the details section for more information
Message ID: {AD19FF31-B1EB-45C2-84C8-717C9AA55E4F}
Instance ID: {6AFEEE47-42DC-4EC7-B4BB-7E674597F5C6}
Error Description: Object reference not set to an instance of an object.

at Microsoft.BizTalk.XLANGs.BTXEngine.BTXPortBase.VerifyTransport(Envelope env, Int32 operationId, Context ctx)
at Microsoft.XLANGs.Core.Subscription.Receive(Segment s, Context ctx, Envelope& env, Boolean topOnly)
at Microsoft.XLANGs.Core.PortBase.GetMessageId(Subscription subscription, Segment currentSegment, Context cxt, Envelope& env, CachedObject location)