Has it worked in the past and now gives this error? Try creating a new profile and testing the new profile. If it works, migrate the email from the old profile to the new one. If the new profile does not work, start outlook in safe mode (start, run, type outlook /safe). If it works in safe mode you probably have a problematic add-in. Disable all add-ins and re-enable them one at a time to find the troublesome one.