package management - Can't download software's from Ubuntu Software center ( 14.04 LTS )

When I tried to install software's (say Play on Linux / Eclipse), The software center says that Available from multiverse source and there is only a button Use this Source. At the same time I can remove softwares which I installed earlier.
I tried via Terminal but it says that

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package`

I tried this answer, But no visible change. the above result repeated and No install button on Software Center