- Go to "Help->Install New Software".
- In the "Work with:" input box, give the URL "http://download.eclipse.org/webtools/repository/helios/".
- Wait for all the package information to be downloaded and select "Web Tools Platform (WTP) 3.2.1" option. If you are planning to use any other package, you can select them. But make sure you select the ones from 3.2.1 version distribution.
- Click on Next and follow the prompt to complete installation.
If you are interested in knowing more about the issue, please refer here.