This can be caused when you are logged in with two or multiple accounts. When you are logged in with multiple Google accounts, add-ons can work properly with only primary account. To workaround this issue/limitation, you can add different profiles on your browser and switch the profile to use add-ons with different Google accounts.
Errors appear also if you have FileDrop installed multiple accounts you are logged in with.
Please make sure you are logged in with only one Google account or switch the profile in your browser as above.
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