If you haven't done so already, I'd say it's time to call Quicken Support on the phone and request help. Let them do a screen share session with you to review the situation on your computer, to determine the nature of the problem and to figure out how to fix it.
Quicken Support:
afcanfield said: Thank you so much! That worked! I can't believe it. Hopefully it will keep working. It was all working earlier last week, and then all of a sudden I had to reauthorize the Investment accounts again. You are a Quicken whisperer Now I have duplicate transactions in the investment accounts. I thought I could either use control or shift and down arrow to select all the consecutive dups, but that doesn't seem to work. Thanks again!
afcanfield said: I looked at the gear icon, but you have to first accept the downloaded transactions into the register, which I didn't want to do. I thought it was more foolproof to delete them one by one before they were accepted.