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Hi Manabu, 

Welcome to Box Community and glad to help! 

You may run these troubleshooting steps to fix this issue, 

• Please ensure your web browser is the latest version of Chrome, Firefox, Safari, or Edge

• Try clearing your browser's cache. If this does not resolve your issue, please proceed to the next step.
• Verify that you are using one of our recommended operating systems.
• Use your alternate browser, machine and/or network connection. 

• Please make sure your firewall is configured accordingly. 
• Disable your plugins,add-ons, extensions in multiple browsers. 
• Restart your machine. 

Hope it helps!