asp.net - Dll library is not detected from the browser -

I am using DLL in my new web process, I have added the DLL as reference, but when I Calling it with the code works fine behind it, it detects the library in my visual studio

But when I run it from a browser, it marks an error:

PD: DLL works fine in my 2nd 2 proyects (wpf & winform)

Someone knows how it can be?

Thank you! And sorry for my English, I'm learning to steal

Do you have the file "copy in the output directory Create "

In your Solution Explorer, click DLL and it will be in the Properties panel located at the top