Facing problem when validating XML with multiple root node Schema

Hello,

I am facing a problem while validating an XML document against a
schema, using JDOM with XercesJ parser.

Description -

My code is consuming XML messages sent over HTTP Connection. I want to
validate the XML messages before parsing the same. For this I have
created a single Schema which defines all incoming XML messages. The
resultant schema has multiple root nodes.

The code validates one root node for an incoming XML mesaage but fails
to validate root nodes of another XML messages.

The error which I get is 

Error: cvc-elt.1: Cannot find the declaration of element 'Request'. at
line 1, column 10 in entity null

The schema does contain a definition for the tag "Request". I have
cross checked it umpteen times.

I shall be thankful if you throw some light on this.

Vineet Chopra