Hi,
First of all, the reason of the problem is, that your orchestration is waiting for another type of message than your Receive Port sends. You must consider that XMLReceive pipeline always tries to detect the type of message with searching for an appropriate deployed schema.
The reason of your SendPort seems to be working (I suppose) that your SP subscribes to everything that comes from your RP, without regarding types of messages.
So, resolutions:
1. If you would like to use types/schemas, than you should create a custom receive pipeline, which creates that type of message your orchestration waits for. You can use MIME/SMIME decoder pipeline component in your custom pipeline.
2. If you would not like using types/schemas, than use PasshThru pipeline in your RP, and set your receive shape to wait for System.Xml.XmlDocument type of message.
Laszlo