Finding your dynamic port — step by step:

1. On the server: Start → All Programs → QuickBooks → QuickBooks Database Server Manager. 2. Click the Port Monitor tab. 3. Find your QB Desktop version in the list. 4. Note the port number shown next to it (e.g., 56729). 5. That number — plus 8019 — are the two TCP ports to open in Windows Firewall as inbound rules. Both Private and Public profiles must allow these ports.

Fixed ports by QB version (for reference): QB 2018: 8019, 56728, 55378–55382 | QB 2017: 8019, 56727, 55373–55377 | QB 2019+: 8019 + dynamic port (check Port Monitor tab). For QB 2019 and later, do NOT guess the dynamic port — always read it from the Port Monitor tab. The dynamic port can change if you use the "Renew" option in QBDSM.

Firewall Port 8019 Blocked

Primary cause A — Windows Firewall or a third-party firewall blocks port 8019, which is QB's Database Server Manager's primary communication port. When workstations can't reach the server's QBDSM on port 8019, the multi-user file-sharing connection fails with -6120, 0. Opening port 8019 (and the dynamic port) as an inbound TCP rule on the server's firewall resolves this.

Workstation Hosting the Company File

Primary cause B — a workstation (not the server) has "Host Multi-User Access" enabled. The workstation's QBDSM tries to serve the company file but lacks the network authority to do so correctly, producing -6120, 0. Disabling hosting on the workstation (File → Utilities → Stop Hosting Multi-User Access) immediately resolves this cause.

Dynamic Port Not Open in Firewall (QB 2019+)

For QB 2019 and later, a second dynamic port (assigned during installation and viewable in QBDSM's Port Monitor tab) must also be open alongside 8019. If only 8019 is open but the dynamic port is blocked, -6120, 0 still appears. Always check both ports.

Damaged .ND or .TLG Files

If the .ND or .TLG files are corrupted while a firewall or hosting issue also exists, -6120, 0 can appear even after fixing the firewall/hosting. Rename both companion files → run QBDSM scan to rebuild them → retry opening the company file from the network.

Company File in a Non-Default or Damaged Folder

If the company file is stored in a folder that doesn't have proper sharing permissions (especially if not in the default QB company files folder), QBDSM can't serve it over the network. Moving the file to the default location (C:\Users\Public\Documents\Intuit\QuickBooks\Company Files\) or setting correct permissions resolves folder-based -6120, 0.

Invalid File Extension

Trying to open a file with an incorrect extension (.qbm, .qbw.adr) in a network context can produce -6120, 0 because QBDSM doesn't recognize the file format for network hosting. Ensure the company file has a .QBW extension before attempting multi-user access.

METHOD 1 Check Hosting on All Machines Workstation hosting — fastest check

METHOD 2 Open Firewall Ports Using Port Monitor Port 8019 or dynamic port blocked

METHOD 3 Rename .ND + .TLG + QBDSM Rescan Companion files corrupted alongside firewall/hosting issue

METHOD 4 Run File Doctor + Check Folder Permissions + Repair QB -6120, 0 persists after hosting and firewall fixed

How is Error 6120, 0 different from Error 6073, 816?

Both can be caused by a workstation incorrectly hosting the company file, but the additional cause and primary focus differ. Error 6073-816 is specifically "more than one computer hosting simultaneously" — the definitive fix is disabling extra hosts. Error 6120, 0 adds a second distinct cause: "firewall port 8019 is blocked" — the error can appear even when hosting is perfectly configured if port 8019 is closed. The diagnostic path for -6120, 0 therefore always includes both a hosting check AND a firewall port check, while -6073, -816 focuses primarily on the hosting conflict. The Port Monitor tab in QBDSM is the 6120-specific tool — it's not needed for -6073 troubleshooting.

What is port 8019 and why does QB need it open?

Port 8019 is the primary TCP port used by QuickBooks Database Server Manager (QBDSM) — QB's multi-user file-sharing service — to listen for connection requests from workstations. When a workstation user opens QB and accesses a network-hosted company file, QB on that workstation sends a connection request to the server's QBDSM on port 8019. The QBDSM then handles the file-sharing session. If port 8019 is blocked by Windows Firewall or a third-party firewall, the workstation's connection request is dropped and QB reports -6120, 0 — it can't even establish the initial handshake with the QBDSM to begin opening the company file. This port is static across all QB versions; it never changes. The dynamic port (viewable in Port Monitor) is a second port used for data transfer after the initial connection on 8019 is established.