This error usually means that the admin$ (admin share) is not allowed or unavailable on the remote PC. Admin$ is required to be available whenever you need to push-install Remote Utilities (or any Windows software) onto a remote machine. Please make sure that admin$ is allowed on the remote machine and you have access to it.
In addition, this error might also be caused by the fact that the disc Z is mapped on the Viewer computer and, therefore, is not available. Please make sure that the Z drive/letter on your Viewer PC is empty and available because the program uses that drive temporarily for the installation/upgrade process.