odd error message from xmlrpc

[David Viner]

i have a script which is using the xmlrpc interface to call xindice (the
setDocument and insertDocument methods).  Occasionally, I get this error
message:
java.lang.StringIndexOutOfBoundsException: String index out of range: -1

and on the xindice console:
Fatal error parsing XML: Document contains illegal control character with
value 0

Has anyone else seen this kind of error message or have any idea on how to
solve it?

dave