When installing the web connector using QuickBooks desktop, make sure to do the following
Make sure the QuickBooks company file you want to connect is open.
You must log in to QuickBooks as an admin.
Make sure you are in single user mode in QuickBooks
Make sure you have only 1 QuickBooks file open.
Watch this video on how to integrate your QuickBooks file with ConnectBooks.
(If you have a filter/Firewall on your pc, make sure the following domains are unblocked.)