Hi Akshaya,
Even I faced the same problem. Looks like in order for the UI Dev toolkit for HTML5 (i.e. SAPUI5 Application Development Plugin) to work, the following eclipse plugins have to be added:
- Eclipse Faceted Project Framework
- Eclipse Faceted Project Famework JDT Enablement
- Eclipse Java EE Developer Tools
- Eclipse Java Web Developer Tools
- WST Common Core
(You can find these from http://download.eclipse.org/releases/juno" or http://download.eclipse.org/releases/kepler")
Once you hae installed these, install the ui5 kit again.
You can also refer SCN thread: