cannot shell this solid...

 From:  Rudy
2015.1 
Hello Guys,
hello Michael.
How are you doing?

Bear with me about my ...well...cannot define it....

I want to shell this solid. I select the flat surface on the buttom, use the shell command, nothing happen.
Why is that?
I tried many tickenesses. Nada

Surely this is stupid.
Thank you much,
Rudy
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