The gwttk 0.2.3 was incompatible with GWT 1.4.60.
I patched the file ExposedCellPanel.java to run correctly on GWT 1.4.60.

The following was changed:

	//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); 

Svetlin Nakov
http://www.nakov.com/blog/
