regular expresion to take an attatched xml document

Hello all. 

I am trying to take an xml document which is included insided another
document for that I am using an state called XML and a regular expresion
like this:

<ESTADO_XML><\?xml(.|\n)*> {....} 

It almost always it works but at times it is not working I can't figure
out what is happening... 

Any help would be very appreciated.


Thank you very much

Rob