On encountering the QuickBooks Error 6123, I figured the reason behind this was the disrupted installation of QuickBooks updates. I found these hacks to useful, you should also give it a try-
Locate your file and Right-click on it.
Rename the file.
Remove special characters from the name that should not extend more than 30 characters.
Close QuickBooks.
Download the QuickBooks Tool Hub.
Open the downloaded QuickBooksTool.exe file.
Follow the wizard to allow the program to finish installation.
After the process is completed, open the Tool Hub.
You can more effective solutions for this error here. Also, there is a technical team available for on-call support at 855-856-0042 anytime.