Flex - Error #1088 On Passing A Class As A Parameter For Web Service In Flash Builder

I need to pass a struct and a string in a web service. I am using a WebService components to do so.upon my search, there is no struct type in actionscript and so I used a class for that one.

public class UserInfo{
public var name:String;
public var dateAdded:Date;
}

and I'm filling it up so that I can pass it on the web service like this:

var newUser:UserInfo = new UserInfo();
newUser.name = "myName";
newUser.birthdate = new Date();
webServComponentId.operationToCall(newUser, "password");

Upon sending this request, it prompts me an error of Error #1088.

the component that is being called by webServComponentId.operationToCall(newUser, "password"); is this:

<s:WebService id="webServComponent" wsdl="[PATH OF WSDL HERE]" >
<s:operation name="operationToCall" result="functionToCallWhenResult(event);" fault="Alert.show(event.fault.faultString)" />
</s:WebService>

Basically it is a web service via MXML. So when I call the operation, it always go to fault part and shows Error #1088