Well, I'm no expert, but have had this problem a few times when importing .QBO files.
Also, when I had previously imported a partial month of transactions (downloaded from bank using transaction dates), and then tried to import the full statement month, I got stuck (though deleting the digit from ACCTID solved that one for me.
These were the steps that were provided by QB for Mac support folks that I used. Step 4 is the one I don't see in your list of what you tried, and when I forgot to do that, it didn't work for me either... Good luck
- From the Company menu, select Chart of Accounts.
- Select the bank or credit card account you want to import the .qbo file into.
- Choose Edit Account then select the Online Settings button.
- From the Download transactions drop-down, choose Not enabled.
- Download a new QuickBooks web connect file from your bank using only the dates you need. Don't go back further to avoid manually matching transactions.
- Open the QBO file in a text editor like TextEdit.
- Scroll down until you see ACCTID and locate your account or credit card number.
- Delete the last digit of your account number then save your changes and close the text editor.
- Import your QuickBooks web connect file and select the correct account.
