Error using Excel 2010 PowerPivot addins to connect to Oracle database

Hi,
I was using MS Excel 2010 with the PowerPivot add-on to connect to Oracle database when I got this error message, see below. I checked Oracle and it seemed working fine. I searched the internet and found a workaround which I followed but couldn’t get it done right.
Can someone help me here, instead? Please help.

PowerPivot for Excel
Failed to connect to the server. Reason: ORA-06413: Connection not open.
