There are several circumstances when users encounter certain errors which make it difficult for them to continue working with the QuickBooks software. One such error is the login error, which is the most common and widespread issue. To fix the same, you must go through the steps mentioned below:
Steps to fix QuickBooks login error:
Step 1: You must close all open QuickBooks processes
Step 2: Prefer rebooting your system and modem/router
Step 3: Make sure that all the security settings are appropriate

In case none of the above solutions helps you fix the login error, you can get in touch with QuickBooks customer service number and explain your problem to a well-qualified expert who will provide you with the best possible solution in no time at all.

close all QuickBooks processes
1) by pressing Ctrl+Alt+Delete, an Open Task manager.
2) Click on the Processes tab.
3) to sort processes alphabetically, Choose Image Name.
4) all processes begin with “QB”, Right-click on them.
5) Click on End Process.