GWT Tk (http://www.asquare.net/gwttk/) is an excellent open-source GWT widget library. I use it to show modal dialog boxes in my GWT applications. There is only one problem: the ModalDialog does not work with the latest version of GWT: GWT 1.4.60. I investigated where the problem comes from and I patched the file ExposedCellPanel.java to run correctly on GWT 1.4.60. Here are the changes:

 //insert(w, null, getChildren().size());
 //Element td = getCellElement(cellIndex);
 //DOM.insertChild(td, w.getElement(), wIndex);

 Element td = getCellElement(cellIndex);
 int childrenCount = getChildren().size();
 insert(w, td, childrenCount, false);

The original author of GWT Tk didn’t publish a new version to support GWT 1.4.60 when it officially released so I provide my modified one here: gwttk-0.2.3-patched.zip.