For this particular database> right click on it.> go to properties>Options> The compatibility level was set to SQL Server 7.0. Changed the compatibility level to SQL Server 2005(90)
Now i am able to view the dependencies. This is how i resolved the issue.
Finding out the external references is a total different scenario. Sometimes some databases may not have any external references at all.
Solution to this has been posted on this blog: http://sqldeveloper9999.wordpress.com/2013/10/18/redgates-sql-dependency-tracker-does-not-show-dependencies-on-a-few-databases/