soap4r authentication error - soap-client

Question

I am using soap4r with ruby 1.8.7p358 and I am facing a strange error. I have an endpoint_url, when I browse it, there is no authentication error message. It prints out the response. However, when I create a soap client and try to access the method of the client, it gives me authentication error.
For instatance:
I have a url (say) endpoint_url.com/api/get_name.php?user_name="test"&api_key="test"
This link gives me response like
<response>
<result>
<success>1</success>
</result>
<userspage="1" numberofpages="1" numberofusers="1"><row>Sadiksha</row>
</domains>
</response>
I initialize the rpc driver as
def initialize
#username = "test"
#apikey = "test"
#driver = SOAP::RPC::Driver.new("endpoint_url.com/api/get_name.php", "urn:UserDetails")
end
I have a method in the same file that gets all the statistics of user
def getStats (name)
#driver.add_method('GetDetails', 'name')
user_details = {
'user_name' => #username,
'api_key' => #apikey,
'name' => name
}
result = #driver.GetDetails(user_details)
return result
end
When I run the program it gives me error "Your username & apikey were not recognised!" I have been looking at it for a sometime now. But, I really cannot figure out what might be wrong! Can anyone please let me know what I am doing wrong here!