This may be caused by Windows Task Scheduler task for the current backup account username.
User-added image

The task has been incorrectly cached in the OS. Because of this, it may or may not exist in Task Scheduler tasks. In this case, you would be unable to complete the backup wizard and receive the following error:

User-added image
In order to fix the issue for the affected username, you need to clean the Task Scheduler cache and fix the transaction log via the following steps:

  1. Check the Online and Recovery Manager task whether that task is for problematic backup account via Taskschd.msc. Remove it if exist.
  2. Firstly Export and after that remove the key via regedit tool %HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Schedule\TaskCache\Tree\Online Backup and Recovery Manager%;
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  3. Type following via CMD prompt : "fsutil resource setautoreset true c:\" and press enter; (article: )
  4. Reboot the computer.
  5. Recreate backup set using the problematic user credentials and check the result.

In case of issue is still persist:

  1. First time complete wizard without option 'Backup automatically without user intervention'Screenshot: .
  2. Enable option during the second iteration Screenshot: .