Hide Cannot GET /template/url.html if template not found


Is there a way to hide/disable error messages in case template file not found?
In case there is a configuration missmatch where an external driver tries to load templates over ACMP that can not be found CasperCG render a “Cannot GET /template/url.html” notice.

Is there a way to display nothing in stead of the error message?

That is not something Caspar does, but probably some client program, that you use. Have you checked if there is a url.html template somewhere in your template folder? If yes, just make it an empty page or delete it.