Problems using Ibatis

Hi,
This is an exception when Ibatis is trying to set a value for a java
bean property.
java.lang.IllegalArgumentException: object is not an instance of
declaring class
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at
com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:
104)
at com.ibatis.common.beans.MethodInvoker.invoke(MethodInvoker.java:
17)
at
com.ibatis.sqlmap.engine.accessplan.PropertyAccessPlan.setProperties(PropertyAccessPlan.java:
46)

is the GAE runtime engine not allowing the action?