QuickBooks error H202 occurs when a user tries to access a QuickBooks company file in multi-user mode, and the computer is unable to establish a connection with the server or host computer. This error can occur due to various reasons such as network issues, incorrect configuration of settings, or damaged QuickBooks installation files.

Here are some possible causes and solutions for QuickBooks error H202:

1. Incorrect hosting configuration settings: Ensure that the QuickBooks hosting settings are properly configured on all computers accessing the company file. You can check the settings by opening QuickBooks and navigating to File Utilities Host Multi-User Access.

2. Firewall settings: Check the firewall settings on the server computer and all client computers. You may need to add QuickBooks as an exception to the firewall or temporarily disable the firewall to see if it resolves the issue.

3. Incorrect DNS settings: Ensure that the DNS settings on the server and client computers are correct. You can check the settings by opening Command Prompt and typing 'ipconfig /all'. The DNS settings should match on all computers.

4. Damaged QuickBooks installation files: Repair QuickBooks installation files by running the QuickBooks Install Diagnostic Tool or by uninstalling and reinstalling QuickBooks.

5. QuickBooks Database Server Manager issues: Restart the QuickBooks Database Server Manager service on the server computer.

6. Third-party antivirus software: Check the antivirus software on the server and client computers. You may need to add QuickBooks as an exception to the antivirus or temporarily disable it to see if it resolves the issue.

If none of these solutions work, you may need to consult with a QuickBooks expert or contact QuickBooks customer support for further assistance.