While editing the user profile in ArcGIS Online for a newly invited member, the following message displays, "You must supply security question and answer," after clicking the Save button even though a selection is made from the Security Question drop-down list, and a value for the Answer field is provided.
When the message is received, click the Cancel button for the message, and then click the Cancel button on the user profile page. The value provided as the answer is saved and can be used. Reset the password by clicking the Forgot Password option while signing in to ArcGIS Online.