Step 1: Ensure there are no pending updates available to Microsoft Excel by referring to this article. If there is, please update them and try again. If you still receive this error proceed to step 2 below.
Step 2: If you are on Windows PC, update your Cache and cookie settings by following these instructions. Once updated try logging into CloudExtend again. (Mac users can skip this step). If you still receive this error proceed to step 3 below.
Step 3: If you are logged into Excel, log out. To do this click on your name on the top right corner of Excel and click Switch accounts. From there sign out of your account. Once signed out you should not see your name in the top right hand corner of Excel any longer. Go to My add-ins and click CloudExtend again. Try to login. If you are able to login successfully contact your Office 365 Admin and ask them to grant you the permissions required to run Office Apps.
Step 4: If you are still not successful contact firstname.lastname@example.org or your Account Manager for further assistance.