This happens when something has changed in the file, such as the account number. And, QuickBooks isn't associating it with your bank account.
To fix this, you'll want to compare the account number from the downloaded file. Simply right-click it and select Open With in Notepad.
Now, look through the list and find the <ACCTID> for the account. On your Chart of Accounts in QuickBooks, right-click (control+click) on the account in question and choose Edit Account. Proceed to the General tab and copy the bank account number.
If the same issue persists, you can create a new bank account in the Chart of Accounts. Open the old one and rename it. Then, merge them so the lighting bold will be removed. All transactions will be transferred to the new online.
I've added these articles for other troubleshooting steps:
RE: Then when I try to deactivate the account, it says there are transactions left
Usually when it says this there are. If you check using the bank feeds feature, are there any transaction to accept (or delete)? If so, then do that and then you should be able to deactivate the bank feeds set up on the account.