imageabotar.com :

Bad news but not really unexpected for me, Ext JS and MyGWT (a.k.a. Ext GWT) have just changed from LGPL to GPL today. In a nutshell, Ext JS and MyGWT are now useless for free commercial use. If you have already based your projects on these libraries, my general recommendation is to continue using Ext JS 2.0.2 until a fork is available or you can transition off Ext JS.

http://abotar.com/blog/2008/04/21/time-to-fork-ext-js-and-mygwt/