User friendly message when the attachment size limit is reached?

We have set a limit to 5MB

When we try to attach bigger files a not very useful error message is displayed

"The website can't be displayed / button text = "diagnosis of connection problems"

We would like to replace this by a user friendly message,

like "The size of the attachment is too big. The limit 5MB...."

Is this possible by adding a parameter in the web.config or by another method ???