Hello there, @paul-s-lofthouse.
We're unable to see the attached file for the error message you've received while reconnecting your bank account to QuickBooks Self-Employed (QBSE). However, if you still want to do so, just select the Reply button below. Then, select the Photos option to insert the file and click Post. Please see the attached screenshot.
Meanwhile, when a bank account is disconnected (deleted) to QBSE, all your transactions under it will be removed permanently. However, once you've reconnected the account, the system will automatically download your recent transactions.
In the meantime, I'm adding this article for the complete list of possible error messages and their fix: Open Banking connection errors. It includes errors like 355, 390, 590, and 571 to name a few.
Once reconnected, you'll have to review and organise your income and expense transactions. This way, you're able to put them on the correct line of your tax form. You can refer to this article for the detailed steps: Categorise transactions in QuickBooks Self-Employed. It also contains instructions about editing or recategorising a transaction.
Additionally, I just want to make sure I've got everything covered. You can also share with me the name of your financial institution. This way, I can provide the exact resolution.
Please let me know how it goes. You can drop your comment below for follow-up inquiries or other banking concerns in QBSE. I'm just around to help. Take care always.