No longer have necessary permission?

Many thanks to those who chimed in to help out.

My son suggested not trying to save the new image to the root drive and voila'. I am able to save it under my user home profile.

I am not sure if that means I still have some issue with permissions/administration or if that is the way things are supposed to work. I suspect it is the latter. If so, Apple may wish to consider modifying the https://support.apple.com/guide/disk-utility/create-a-disk-image-dskutl11888/mac document where is says, "...then choose where to save it.", to be more specific so that others attempting to do so don't encounter similar difficulties.

Anyway, happy to be able to move forward. Thanks again to those who contributed ideas/suggestions.

Thanks : OS 10.14.6 on a MacBook Pro 13" Retina Early 2015.

It is in step 9 of the linked document you provide that the problem arises. I no longer have permission to write the created image to my HD (1TB Flash Drive). But, I can save new documents to it, no problem.

When I unlock the Users & Groups for the current user (me), the 'Allow user to administer this computer" is checked but remains dim (see image).

Thanks. I did try to the internal drive first (and several times). I really needed it on the internal drive. I just tried the external drive as a part of my troubleshooting. The external drive format is Mac OS Extended (Journaled).

With the internal HD I get the message on the attached image. With the external drive I get a -5000 message.

Thanks Leroy. Had that as my last resort plan, but may go ahead and give them a call up front. I did come up with this, however, and am wondering if it would work:

1) After backing up to both my Time Machine and my external clone, restore the MBP/OS with a new administrative account.

2) Use migration assistant to transfer everything but the Computer & Network Settings.

Any idea whether this would work?