Whys is the program closing when accepting new transactions?

Have you followed the instructions and reinstalled Quicken before running Validate + Supervalidate?

If Quicken crashes during Validate or immediately after Validate while reopening the data file, I can only assume that your data file is damaged beyond repair and needs to be restored from a recent Manual or Automatic Backup, taken before the crash problem turned severe.

I installed the manual update of the latest version as directed in your first reply. I then ran validate and super validate, and had the same problem with each. I am going to uninstall and re-install quicken with the latest updates and then attempt to restore from a manual update taken before this mess started, unless you direct me otherwise. A prompt response would be greatly appreciated.

You can try a complete uninstall, reinstall procedure and then restore your data file from a backup taken before this all started. When restoring, change to a different file name and leave the current (broken) data file untouched. Don't overwrite it.
You may have to go back in time to successively older backups until you find one that works.

While on the subject of problems, I am having repeated problems with getting my 6 American Express cards bills loaded properly for the correct card, and having the ability to Quick Pay from within Quicken. Right now, I have to pay from the Amex site, which makes having the Premiere subscription useless for paying bills, as my Chase, Citi, and now Amex cards all have to be paid either by check pay or payment from the various websites

This is the subject of many other discussions here in the community.
If your bank (the one that runs your checking account) recently required you to reauthorize your checking account and/or your bank has changed from "Direct Connect" to either "Express Web Connect" or "Express Web Connect+" you can no longer use Online Bill Pay direct to the bank or Quicken Bill Manager's Quick Pay function. The bank no longer supports this function through Quicken.

IMHO, you have these alternatives (in no particular order of preference):

1. Use Quicken Bill Manager's Check Pay making sure to submit payment early enough (at least 3 weeks before due date) to allow time for delivery and processing. Note: limited number of free transactions per month.
2. Logon to the bank's website and schedule your bill pay payments to be executed by the bank from your checking account. In parallel to that, in Quicken use a regular Scheduled Reminder to record your payment. Repeat both actions every time another payment is due.
3. Bypass Bill Manager. Let the biller's (or credit card company's) computer system do all the work for you. Logon to the biller's website once and set up their Autopay, APS, Direct debit, etc. service to make the current payment and all future payments on Due Date directly from your checking account. In parallel to that, in Quicken, every month, record a regular Scheduled Reminder to keep track of your payments before they come due.
4. Write (or print with Quicken) a paper check and mail it to the biller, making sure to mail payment early enough (at least 10 days before due date) to allow time for delivery and processing.

I've been using method #3 for decades, since before the Internet and transaction download capabilities were even invented. It's easy to get used to this process. And I have yet to miss a single payment.