1998 Buick Century EGR Valve Replaced. Still getting EGR V

Engine Performance problem
1998 Buick Century 6 cyl 99,000 miles

The car was reading the code of an EGR Valve error, so I replaced it. I reset the check engine light and it went back on, so when I took it back to get the code read at Auto Zone, they told me it was still reading an EGR valve error code.
I was told by the guy at the store I should clean the EGR Valve pipe but I needed some gaskets from the dealer?

I'm really confused and need to get the car inspected, can anyone help?

Thank you.