I remember a similar case using a RichTextEditor, and the problem was the frame, to type something in the RTE I had to access the frame, looks the this line
vSelenium.Type("//body", "Selenium Question!");
I did the following in C#
// Add the Question in the RTE
vSelenium.Click("//div[@id='math_help_problem_question_tab_header']/span[2]");
Thread.Sleep(2000);
vSelenium.SelectFrame("question_rte");
vSelenium.Type("//body", "Selenium Question!");
vSelenium.KeyDown("//body", "!");
vSelenium.KeyUp("//body", "!");
Thread.Sleep(5000);
vSelenium.SelectWindow("null");
vSelenium.Click("//img[@onclick='javascript:submitQuestion();']");
Thread.Sleep(5000);
Assert.IsTrue(vSelenium.IsElementPresent("//a[contains(text(),'Selenium Question!')]"));
Assert.AreEqual("Selenium Question!", vSelenium.GetText("//a[contains(text(),'Selenium Question!')]"));
maybe that helps...
Thanks