A byte does not support arithmetic.

See http://stackoverflow.com/a/941627/90882 for reasons why a byte does not support arithmetic.

This was causing the acceptance test to fail in certain circumstances.
Here is the error that could happen:
System.Runtime.Serialization.SerializationException: An error occurred while attempting to extract logical messages from transport message NServiceBus.TransportMessage ---> System.Xml.XmlException: Data at the root level is invalid. Line 1, position 1.
   at System.Xml.XmlTextReaderImpl.Throw(Exception e)
   at System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()
   at System.Xml.XmlTextReaderImpl.ParseDocumentContent()
   at System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace)
   at System.Xml.XmlDocument.Load(XmlReader reader)
   at NServiceBus.Serializers.XML.XmlMessageSerializer.Deserialize(Stream stream, IList`1 messageTypesToDeserialize) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\Serializers\XML\XmlMessageSerializer.cs:line 292
   at NServiceBus.Unicast.Messages.ExtractLogicalMessagesBehavior.Extract(TransportMessage physicalMessage) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\Unicast\Messages\ExtractLogicalMessagesBehavior.cs:line 74
   at NServiceBus.Unicast.Messages.ExtractLogicalMessagesBehavior.Invoke(ReceivePhysicalMessageContext context, Action next) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\Unicast\Messages\ExtractLogicalMessagesBehavior.cs:line 52
   --- End of inner exception stack trace ---
   at NServiceBus.Unicast.Messages.ExtractLogicalMessagesBehavior.Invoke(ReceivePhysicalMessageContext context, Action next) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\Unicast\Messages\ExtractLogicalMessagesBehavior.cs:line 58
   at NServiceBus.Sagas.RemoveIncomingHeadersBehavior.Invoke(ReceivePhysicalMessageContext context, Action next) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\Sagas\RemoveIncomingHeadersBehavior.cs:line 23
   at NServiceBus.MessageMutator.ApplyIncomingTransportMessageMutatorsBehavior.Invoke(ReceivePhysicalMessageContext context, Action next) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\MessageMutator\ApplyIncomingTransportMessageMutatorsBehavior.cs:line 22
   at NServiceBus.UnitOfWork.UnitOfWorkBehavior.Invoke(ReceivePhysicalMessageContext context, Action next) in c:\BuildAgent\work\31f8c64a6e8a2d7c\src\NServiceBus.Core\UnitOfWork\UnitOfWorkBehavior.cs:line 24/n/r

This error was occurring in the SqlTransport, my guess is that by doing the arithmetic on the byte we were create a byte that was outside the range of valid bytes that SqlServer can serialize.