Thanks for all of the replies. I was finally able to find it. I did as suggested and saved a copy of the plan file and started deleting things until the error disappeared. For the benefit of those who may also encounter this I will share what I found.
The felonious polyline was just a regular rectangular polyline. It had a corner jutting out a little bit that needed zooming in to see it. But, it was in a cad detail window and the error would pop up in any part of the program, showing up immediately when opening the plan file, or when bringing up a view. Eventually the program would halt with major system failure. It did look like the aforementioned circle would pop up very quickly before the error message, then disappear.
I had spent two days with a client working on this drawing, which was a very detailed and complex plot plan with survey data and a lot of grading stuff - this was about the third iteration of trying to figure out where to place the house, the "causeway", and the garage,. Basically it was him standing over my shoulder telling me what to draw where. As it happens I'm one of those who spent two years learning AutoCAD and am still struggling to get a grip on CA CAD, so it was less than a joyous occasion. When the error first popped up it wasn't an ideal situation to suddenly stop and go into troubleshooting mode.
Now I try to finish up this project while interviewing for jobs in a totally different line of work.
StevenYaple's post in Error: This Standard Polyline Overlaps Or Crosses Itself was marked as the answer