Your structure should be:
src
|-- mystock
|-- client
| |-- Stockexample.java
| |-- LoginGWT.java
|-- StockExample.gwt.xml
If thats your structure, does the error go away if you add <source path="client"/> to your StockExample.gwt.xml? Following the documentation it should implicitly be set in the module if you do not specify any <source> but maybe thats not working anymore.
If that does not work you probably have a different error that is causing the "no source available" error, so you should see if you can get more error information in the development mode / console view in Eclipse.
-- J.