The QuickBooks connection has been lost error typically arises due to issues with network connectivity or QuickBooks configuration. Here’s how to resolve it:

1. Check Network Connection: Ensure your internet connection is stable. If you're using a network, verify that all network cables are securely connected and that your router or modem is functioning correctly.

2. Verify Hosting Settings: If you're using QuickBooks in a multi-user environment, make sure that hosting is properly set up. Check if QuickBooks Database Server Manager is running on your server and that all necessary ports are open (default is port 8019).

3. Restart QuickBooks Services: Close QuickBooks and restart the QuickBooks Database Server Manager and QuickBooks services. This can help re-establish the connection between QuickBooks and your company file.

4. Update QuickBooks: Ensure that you have the latest version of QuickBooks installed. Updates often include fixes for known connectivity issues. Go to the QuickBooks menu, select ‘Help,’ and then ‘Update QuickBooks.’

5. Check for Firewall or Antivirus Interference: Sometimes, firewalls or antivirus software can block QuickBooks from connecting. Temporarily disable these programs to see if the issue persists. If it resolves, add QuickBooks to the exception list in your firewall or antivirus settings.

6. Rebuild the Data File: Corruption in your company file can also cause connectivity issues. Use the built-in ‘Verify Data’ and ‘Rebuild Data’ tools in QuickBooks to scan and repair any file corruption.

If the problem persists after trying these solutions, consider contacting QuickBooks support for further assistance.