George, Harish
That is a very old Wiki and only applicable for XI3.0/PI7.0.
Mapping-based message split (multi-mapping) for IDoc receiver is supported at least from PI 7.11 (I didn't work on PI 7.1 so I'm not sure.) From PI 7.11 onwards, it is easily achieved by just changing the signature of the IDoc receiver to unbounded - no longer any need to export and edit the XSD.
1-n multi-mapping for IDoc targets is a very common scenario and I've done tonnes of them without any issue. The IDoc receiver channel (whether dual stack or AAE) automatically unwraps the <Message>/<Message1> tags into child messages.
Here is a simple sample that I just did on PO 7.4 system with IDoc_AAE receiver adapter.
Set target occurrence to unbounded
After mapping payload shows that the <Message>/<Message1> sections are added to indicate multi-mapping message split.
Log of parent message shows a split to child messages.
Child payload shows that the <Message>/<Message1> tags are automatically removed.
Log of child message shows that child message is successfully sent as IDoc to backend system.
From your error above, it looks like it's related to incorrect target payload. At position 68 of the payload it is expecting an end tag but getting an x (unicode 0078) instead.
Invalid XML 1.0 character encountered within IDocXML for type <ns0:Messages>:
state=EXPECTING_IMMEDIATE_TAG_END, charPosition=68, lineNumber=1, columnNumber=69, invalidChar=U+0078,
The "standalone=no" in your payload indicates that you might be using a Java mapping to perform the multi-mapping. Check if the output of the mapping is in a correct XML format. Check also that your Operation Mapping is using unbounded occurrence for the target operation.
Rgds
Eng Swee