OpenSAML user discussion

I apologize if this has been dealt with before. (I am still trying to find my 
way around this list- newcomer).

I am using CAS for SSO which in turn uses opensaml-1.1b. I have a strange 
problem where in calling SamlResponse.toString() apparently throws an 
exception-

2008-06-18 12:23:01,239 ERROR [org.opensaml.SAMLResponse] - <caught a SAML 
excep
tion while serializing XML: org.opensaml.MalformedException: 
AttributeStatement
is invalid, requires at least one attribute>

There is certainly an attribute, among other fields, that are set before the 
toString() call.

I am running under tomcat6 and the xml libs are those that came with the 
opensaml distribution.

Thank you for your time.