KB3181988

https://support.ncomputing.com/portal/kb/articles/too-many-users-logged-in-to-windows

KB 2984972,  KB 3003743

https://support.ncomputing.com/portal/kb/articles/new-9-28-2016-microsoft-kb3181988-vspace-host-freezes-or-devices-will-not-connect

https://support.apple.com/en-us/HT204088

http://thenextweb.com/microsoft/2016/08/01/missed-the-windows-10-update-deadline-you-can-still-upgrade-for-free/#gref

https://community.intuit.com/articles/1437462-configure-firewall-and-internet-security-settings-for-quickbooks-desktop​

Configure your 3rd Party AntiVirus/Firewall Programs

Note: Only perform this if configuring the Windows Firewall does not resolve the issue.

• Due to the vast number of firewall programs available and their ever changing versions, Intuit is unable to provide additional configuration steps. Refer to your software’s documentation or the software publisher’s web site for support.
• Intuit does not support or maintain steps on the various internet security programs on the market today. In most cases, you should be fine just adding the ports above to the Windows Firewall. If you still encounter errors opening a file over a network or multi-user problems, you may want to try adding the following executable/directories to your 3rd party virus program.

Add the following ports to your 3rd party Antivirus/Firewall:

Make sure TCP is selected and type in specific ports needed for your QuickBooks year version: (if you have multiple year versions of QuickBooks Desktop installed or will be using, you will need to add each year’s ports as well in this format: 8019, XXXXX, XXXXX, XXXXX, XXXXX).

• QuickBooks Desktop 2018: 8019, 56728, 55378-55382
• QuickBooks Desktop 2017: 8019, 56727, 55373-55377
• QuickBooks Desktop 2016: 8019, 56726, 55368-55372
• QuickBooks Desktop 2015: 8019, 56725, 55363-55367

Add the following executables to your 3rd party Antivirus/Firewall:

Note: If you see Program Files (x86), go there as that means you are on a 64-bit Operating system.