Hmm... I think if you turn on developer Debugging for your site, you might get a more detailed error message (the message is deliberately vague to avoid sharing security-sensitive data when developer debugging is off).
At the moment, it could be any of a lot of issues: invalid/expired token, IP address restriction, webservice not enabled, webservice function not included in enabled webservice, webservice user not having the right capabilities to undertake the action requested, webservice not allowed for the given user, etc.
At the moment, it could be any of a lot of issues: invalid/expired token, IP address restriction, webservice not enabled, webservice function not included in enabled webservice, webservice user not having the right capabilities to undertake the action requested, webservice not allowed for the given user, etc.