[V8i SS10] Attaching WMS?

I've begun delving into WMS imagery as a source for our projects. I prefer it to any static imagery for many many reasons.

As far as I know, you find the link to the WMS server (something like https://tnmap.tn.gov/arcgis/services/BASEMAPS/IMAGERY_WEB_MERCATOR/MapServer/WMSServer), type it into the dialog for WMS attachment, and the connection is made, and you have an image.

But it doesn't always work. Quite often I will come up with a server error: The underlying connection was closed: An unexpected error occurred on a send.

I have no idea what that means or how to troubleshoot it. I have no idea if there is a workaround, a setting or other option I should be using.
I know the WMS server is valid because I can see it in other programs.