XMLCoder decode invalid data type: com.wm.lang.xml.Document

Hello,

when my customer send me purchase order that begin with:

<?xml version = '1.0' encoding = 'ISO8859-2'?>

SAP business Connector 4.6 SR1 (webmethods Integration
Server 4.6 embeded) produce erroe in server log:
[B2BCORE.0076.0007] XMLCoder decode invalid data type:
com.wm.lang.xml.Document
and doesn’t parse xml document send by http protocol.
But, when I test sending same document but with modified
first line:

<?xml version="1.0" encoding="ISO8859-2"?>

everything works fine. Problem is that first line is
generated automaticaly and this worked till a few days ago.

Please help
Mladen