Other authors have reported similar things only to discover that it just took a little longer for everything to appear. PubIt! says it can take up to 72 hours before everything is "live" when you put an ebook up for sale. Some authors have reported delays of weeks (but I think that is rare). Part of the problem may be that B&N is still getting things back together after the recent hurricane damage (they are located in New York).
As for the "Technical Difficulties" message, no one knows what it means. My wife received the message when uploading a recent book. Yet her book went live in a day and a half with no apparent problem. In her case the "Technical Difficulties" message meant nothing.
Regardless of the reasons, you just have to be patient. Your cover will probably appear in the near future.
Kind regards, David
Thanks so much. I'll wait and see what happens.