It sounds like your user tried to execute the microflow GetAccountFromCurrentUser but does not have permission to do so. Usually, a button to invoke a microflow like this would be hidden if the user couldn't access it. Did you manually force it to be visible? The other way this can happen is if a microflow is called from java using the user's security context.
Hopefully that gets you going in the right direction. If you're still stuck, please explain how this microflow gets triggered by the user and we'll try to get you sorted.