This problem may be solved by updating your browser to the latest version, or using other browsers. The system requirements of KUMOI depends on Office365 because KUMOI uses Office365 for Education operated by Microsoft Corporation.

Internet Explorer - The latest version and one version before the latest one
Firefox, Chrome, Safari - The latest versions.

If the problem is still not solved after you update your browser to the latest version, disabling some add-ons or extensions may help to resolve the issue. The following is the procedure to disable add-ons in Internet Explorer 11.

• 1. Click [Tools] - [Manage Add-Ons] on the upper menu or a gear wheel icon and choose [Manage Add-Ons]
• 2. You see a list of add-ons installed. Select add-ons enabled and click [Disable] one by one. Some add-ons requires to restart the browser for disabling.