Still having Online Issues

During One Step Update from Quicken on your desktop / laptop, if you get error CC-501 for all of your Express Web Connect - connected accounts from several banks while other bank accounts using Direct Connect or Web Connect work OK ...

Please do not use any "Reset CC Credentials" instructions found here in the Community to correct online banking errors.  Instead, please contact Support.
Support has access to a tool that can "reset" the User profile internally on the server.

https://www.quicken.com/support#contact-support

In case of CC-501, 502, 503, 506 errors from a single bank deactivate all accounts with this bank using the same bank logon ID, including any old, long closed, hidden and forgotten accounts that might still be activated. If you miss one, the server involved in handling Express Web Connect - connected accounts will not start with a clean slate and you will continue to have problems. When done, restart Quicken and reactivate accounts.

To deactivate an Account

Go to Tools > Account List.
Click Edit for the account you need to change.
Click Online Services tab.
If the account has been activated for Online Bill Payment, deactivate this service first.
Click Deactivate button in Online Setup box.
Repeat for any other accounts that need to be deactivated.
Restart Quicken to make sure that the changes are fully applied.

To (re-)activate accounts for downloading

Create a backup of your Quicken data file. This is a restore point, should something go horribly wrong during the next steps.
If you normally automatically accept downloaded transactions into your registers I recommend you turn this feature off now. The first transaction download after every activation will download 60 - 90 days worth of transactions into your account(s). Auto-accepting them will most likely create a horrible mess that's difficult to undo. You're better off manually reviewing and accepting or deleting this first batch of downloaded transactions, one by one.  Go into Edit / Preferences / Downloaded Transactions. Remove the checkmarks from both "After downloading transactions" settings.
Go to Tools / Add Account to reactivate the accounts. As you go thru the setup process, Quicken will identify all accounts it can download.
Select an account type, e.g. Checking
Enter the name of your bank and click Next.  Some banks have multiple choices, Consumer vs. Business accounts, Express Web Connect vs. Direct Connect. Be sure to pick the correct one.
Enter your credentials, select Save this password (if using password vault) and click Connect.

You should now see a list of all accounts found at your bank that you can activate. If you are activating an existing account, make sure the dropdown button for that account says LINK. If it says ADD, change it to LINK and select the correct Quicken account.  If it already says LINK, click the button and select the correct existing account register. If you do not do this, then the account will be added as a new account instead of being linked to the existing account register.

Repeat this step for each account listed.
Change ADD to IGNORE for any account on the list that you do not want to activate at this time. You can always come back and activate more accounts later.
Click Next to continue.