The error "Technical error unable to load form" in PrestaShop 1.6 can occur due to various reasons. Here are some common solutions:
1. Clear the cache: Go to Advanced Parameters > Performance and click on "Clear cache."
2. Check file permissions: Ensure that files and directories have the correct permissions (typically 755 for directories and 644 for files).
3. Disable non-native modules: Temporarily disable any recently installed or updated modules to see if they are causing the issue.
4. Verify database integrity: Use phpMyAdmin or a similar tool to check the database for any errors.
5. Update or reinstall PrestaShop: If all else fails, consider updating to the latest version or reinstalling PrestaShop.