PageRequestManagerParserErrorException when using a webpart

[rote]

I'm trying to use jan's wonderful SmartPart from
http://weblogs.asp.net/jan/archive/2007/02.aspx
After trying the Connections Demo from the site and making a connectable
webpart
When using the UpdatePanel i get the error
Sys.WebForms.PageRequestManagerParserErrorException: The message received
from the server could not be parsed. Common causes for this error are when
the response is modified by calls to Response.Write(), response filters,
HttpModules, or server trace is enabled.
Any ideas on how to fis this?
Thanks in Advnace