[caio80]

Try with the PrintWriter.println function, you've got more control when debuggin.

        PrintWriter pw = response.getWriter();
        pw.println(msg);

And try to call your JSP from a JS, like this:

[...]
    AjxRpc.invoke(requestParams, serverURL, reqHeader,  new AjxCallback(this, this._resultCallback), false);
[...]
It_Open1_Zimlet.prototype._resultCallback = function(result) {
    this.displayStatusMessage(result.text);
};

You gotta peek around the Zimbra source code a bit to get the hang of it... Try by first checking ZmZimletBase.js, one of the most important ones.