Problem dealing with large XML documents

I’m doing large document handleing.
I’ve done all the configurational stuff with the wmTN\properties.cnf and the <integration>config\server.cnf files.

Now when i’m subbmiting the xml file to TN, the document is being recognised as large doc and its persisted onto the hard disc. The processing rule is invoking a service which actually does the massaging of the data.
In that service i’m using getContentPartData service, when i’m using bytes in the getAs field and specify the number of bytes i want to retrieve then i’m able to get the data. The problem is, when i’m using stream in the getAs field its throwing an EXML Exception. It says
““Error retrieving content of content part xmldata of document 5enfbt00uruseqke0000001h””
Could anyone help me out with the problem.
What would be the various steps i’m supposed to take care of.