visual studio 2010 unable to start program .dll

I have a problem for my visual studio 2010. When I click start debugging button and it's start debugging.

It seems that there is no error "i just create one "button" on it "

But it will show Unable to start program 'c:\users\.....\xx.dll'

Does someone now how to solve it?

The second question is: when I click left button to see the "Button" source code, why it will show all this project code? Should I revise some setting?