Hello,
How to set disk permissions is described in our
documentation.
However, in the path I see the CMSVirtualFiles - this indicates that you are running on a pre-compiled project or maybe medium trust where the access to the disk is limited. In this case, you need to save the page template on the development/staging environment, save the virtual objects to disk again and deploy it to the live environment.
Best regards,
Juraj Ondrus