Suddenly cannot access file from two computers at once

Open the sample file in the multiuser mode. Did you encounter the same problem?

Good morning, @foodsunlimited. 

Welcome to the QuickBooks Community! Let's work together to figure out why this is happening with your company file. 

Using the QuickBooks Tool Hub should help fix these errors that are occurring. Here's how: 

1. Close QuickBooks.
2. Download the most recent version (1.6.0.8) of the QuickBooks Tool Hub. Save the file somewhere you can easily find it (like your Downloads folder or your Windows desktop). Note: If you've installed Tool Hub before, you can find out which version you have. Select the Home tab. The version will be on the bottom.
3. Open the file you downloaded (QuickBooksToolHub.exe).
4. Follow the on-screen steps to install and agree to the terms and conditions.
5. When the install finishes, double-click the icon on your Windows desktop to open the tool hub.

The networking issues tool within the hub would be the best to use for this situation.

Please let us know how these steps work for you. I'm only a post away! 

Yes, we just tried this and encountered the same issue.

Yes, we have just tried this and encountered the same problem.

Next troubleshoot, you can install the trial version of QB Desktop 2019 to isolate the problem.

We value your efforts in performing the initial troubleshooting above, foodsunlimited. Let's continue with the additional steps below to ensure you can effectively address the error you encounter.

In QuickBooks Desktop (QBDT), error codes 6190 and 816 indicate an issue with your multi-user network. Since these errors continue to occur even after using the QuickBooks Tool Hub, let's do a full reset with your system.

If you've chosen QuickBooks Enterprise Hosting over a server computer, get help restarting the service from our chat support team. While for hosting managed by affiliated Intuit Hosting Providers or another online platform, connect with them directly for technical assistance.

Here's how to restart all of your computers and servers:

1. Restart the server computer, which is hosting the company files.
2. Restart each workstation, which computers are connected to the network that isn't hosting the company files.
3. Open QBDT on the server computer, then the application on each workstation.

Moreover, you can proceed to Solutions 3 and 4 in this article to determine your next step if the issue persists: How to fix Error 6189, 816 and 6190, 816.

Furthermore, improve your efficiency in managing financial information by employing QBDT's Multi-Monitor mode. This feature allows you to work across multiple screens when performing specific tasks on your company file.

You can rely on us to offer further help resolving issues related to multi-user mode in QuickBooks Desktop. Please post your inquiries directly on this thread, and we'll equip you with all the necessary data and resources.