On Quickbooks Desktop:
1. Try resetting the Intuit Sync Manager:
Help > Manage Data Sync > Clear Sync Settings
After doing so, you can relaunch your sync manager by going to:
File > Sync > Launch Intuit Sync Manager
2. Try closing the program and restarting the computer.
3. Oftentimes, a problem may be due to a conflicting firewall. You can try turning off any antivirus or Windows firewall.
4. Sometimes sign in problems are caused by not using the correct email (there will be a related error message). You can find out what it is by calling Intuit at 1-800-4INTUIT, asking for connected services, and providing your: Quickbooks license number, name of business, and name on your account.