Hi,
Create a solution for Contact entity.
1.Import ribbon Workbench solution.
2.Open your Solution in Ribbon workbench.
3.Go to buttons on Home Page .
4.Check if buttons Proerties like Images(16x16,32x32)and JavaScript libraries are correct or not.
5.Update them as required.
Hope it helps,
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http://microxrm.blogspot.in