I had the same problem when I followed the GWT tutorial and fixed the problem.
You can go:
Eclipse → Help → Installing New Software → Working with
Then paste any of these URLs, but change the indigo or helios for your distribution of the Eclipse IDE.
Indigo Update Website - http://download.eclipse.org/releases/indigo/
http://download.eclipse.org/webtools/repository/helios
Wait and Eclipse will show you all the options.
Check the option:
Web, XML, Java EE, and OSGi Enterprise Development
Then click Next, Apply, and Finish and restart the IDE to see the changes.
Everything.
Sofia source share