I am guessing its because you have already opened the stream by calling the resp.setContentType("text/plain"); method, and are then trying to get a Writer object. You can either use Stream based classes, or Writer based classes - not both.
see also: https://groups.google.com/forum/#!msg/google-web-toolkit/siwO-JRggrA/q8LyPbhaIHwJ
We need to apply properties of children first and then shared properties.
For example in service task we parse wsdl and data input and output generated by code then.
Upgrade to Ext JS 2.3.0 was very simple but develop any change at 2.0.2 because it has any document was very hard.

Now you can see:
http://dev.sencha.com/deploy/ext-2.3.0/docs/
http://dev.sencha.com/deploy/yui-ext/examples/samples.html
and all in lib.
Thanks.