Dali, the Eclipse plug-in that supplies the entity generation wizard you are using, relies on another Eclipse plug-in, DTP, to provide the database metadata necessary to perform the entity generation. As a result, this problem could be caused by either plug-in.
A simple way to (possibly) isolate the problem is to use DTP's Data Source Explorer view to see what DTP is returning in the way of metadata. Use this view to connect to your database. (You will be using the same connection profile you created in the Dali Entity Generation wizard.) Once you are connected you should be able to expand the tree to see your tables. If there are no tables, the problem is with the DTP adapter used to retrieve metadata from your database and this is a problem with DTP; if there are tables in the tree, the problem is with Dali.
Also, you should look at the Eclipse log (./.metadata/.log) to see if any sort of exception occurs when you are using the Dali wizard.