There are a few things that can cause this but the most likely issue is going to be if you are manually scoping your developer credentials and you are missing some of the required scopes.

We have sent out several notices since last summer about updating the Upload / Embed Image tool. Part of that process includes shifting over to the inherited scoped credentials that we have available through Canvas. Using those inherited credentials is the best way to keep the permissions where they need to be for the tools.

The March 1st DesignPLUS release included enhancements to the Multi-Tool that allows us to duplicate all of the settings from template assignments, discussions, and pages including grading rubrics and external LTI assignments like Canvas' new quizzes. That additional functionality was a result of convincing Canvas to add some new API endpoints which needed to be added to the scoped credential list. We worked with Canvas to add those scopes to the inherited credentials, but we also included messages about the new credentials in the March 1, 2021 release notes and the Developer Key Scoping page in our Admin Guide. We also posted notices about it on the Cidi Labs Slack channel and even a note about it at the bottom of the Multi-Tool.

We highly recommend you transition over to the inherited scoped credentials. Instructions for updating can be found in the UEI update instructions or on the Developer Key Scoping page.

If you would like help with that transition, please let us know and we are happy to jump on a call to walk you through it. As I mentioned earlier, this is the most likely reason that message is showing up. If it turns out to be something else, it might be tied to the user's browser and/or firewall settings and we can arrange a call to troubleshoot that as well.