Hi, Rob Grae
This error is often caused by a sign-in or account-session problem rather than Windows Defender protection itself. It can also be a temporary service-side issue if the same error appears on multiple devices.
Besides the solutions provided by the Q&A Assist, here are some suggestions you can try:
Confirm that Defender is signed in with the Microsoft account that owns the active Microsoft 365 Personal or Family subscription. Sign out of any other Microsoft accounts first.
Open Microsoft Defender in an Edge InPrivate window. If it works there, clear the cookies and cached data for Microsoft sites in your regular browser, then sign in again. This resolved a similar identity-monitoring issue where Defender had silently used the wrong Microsoft account.
Test the feature from the Defender web portal or the mobile Defender app. A recent case showed the web version working while the Windows app continued displaying the same error, indicating an app-side or temporary service issue.
If only the Windows app fails, go to Settings > Apps > Installed apps > Microsoft Defender > Advanced options, then select Repair. Use Reset only if Repair does not help, as Reset removes the app’s local settings and sign-in state.
If the error also occurs on the web and mobile, submit it through Defender > Profile > Help and feedback, including a screenshot and the approximate time the error occurred. This will likely require an account-side investigation rather than further Windows troubleshooting.
Thank you for your patience in reading, I hope this information has been helpful to you.
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