Like any other problem that arises in an application; the QuickBooks Error 9999has multiple reasons and solutions. There are many solutions that you will have to figure out to fit your situation. Now, there can be a lot of different ways to fix this problem. Here are some of the common and simple ways.
First of all you can try to update your banking details on your Quickbooks Desktop. There can be some mistyping or error in details.
Then you can also clear the browser’s cache files from the browser you have been using.
Trying to fix this problem by disconnecting and then reconnecting your bank account can also be a simple way out.
And then you can also connect with your bank to know what exactly got wrong and has been causing this issue.