Soap Action not parsed as expected

For some reason, if I try:

response = client.request 'Security_Authenticate' do

It doesn't work, the response returns any random fault message. However, if I specify the SOAP Action URL:

response = client.request 'http://webservices.xxx.com/whatever' do

it works perfectly.

Is this a Savon issue parsing the wsdl?

RESOLVED: I had to use lowercase for the action!