Thanks to both gilby and DrByte

First, I carefully repeated the edits to cache.php and sessions.php to make sure I hadn't messed up in making the changes. Still the same results: admin works fine with the edits until config.xsell.php is dropped into the auto_loaders folder. The only change is in the error message. Now returns: "WARNING: An Error occurred, please refresh the page and try again."

Next, I searched and found in phpmyadmin the MIN_DISPLAY_XSELL configuration entry and deleted it. No change, same result. Then I also deleted MAX_DISPLAY_XSELL to see if that might help. Same results. Same error message.

Again, I'm stuck. I appreciate the suggestions and am open to whatever else anyone can suggest.