I have an Apex method that is marked as a remoteAction which is attempting to take two parameters: a Lead and a List of custom objects ("Custom_Object__c" isn't the real object's name, just changed to protect the innocent);

@RemoteAction
public static Boolean insertData(Lead l, List<Custom_Object__c> customObjects) {
   // insert the Lead
   insert l;
   // assign the lead Id to each custom object in the list
   for(Custom_Object__c c : customObjects) {
      c.Lead__c = l.Id
   }
   // insert the custom objects
   insert customObjects;
   // return true (just for example)
   return true;
}

 Over in Javascript, I'm calling this remoteAction with the following data:

// sample data
var lead = {
   FirstName = 'Test',
   LastName = 'Test',
   Company = 'Test',
   Email = 'test@test.com',
   Phone = '555 555 1212'
};

var customObjects = [
   {
      Custom_Field1__c = 'A',
      Custom_Field2__c = 'B'
   },
   {
      Custom_Field1__c = 'A',
      Custom_Field2__c = 'B'
   }
];

MyApexClass.insertData(lead, customObjects, function(result, event) {
   // this would be the callback mojo
});

This code will make it as far as the insertData method, but I get the following error:

Visualforce Remoting Exception: undefined

I tried changing the insertData method to take the second parameters as List<sObject> instead of List<Custom_Object__c> (and modded the code to use dynamic DML to support this), but then I get this error:

Visualforce Remoting Exception: Unable to determine SObject type: SObject.  Please provide an 'id' or 'sobjectType' value.

I interpret this error as needing to supply a 'sobjectType' property to either a) the elements in my "customObjects" array or b) the array itself. I've tried all of the following permutations but still get the same error:

// ... add the property to the element doesn't work
var customObjects = [
   {
      Custom_Field1__c = 'A',
      Custom_Field2__c = 'B',
      sobjectType = 'Custom_Object__c'
   },
   {
      Custom_Field1__c = 'A',
      Custom_Field2__c = 'B',
      sobjectType = 'Custom_Object__c'
   }
];

// add the property to the array doesn't work
customObjects.sobjectType = 'Custom_Object__c';

// for fun, tried to indicate that it's a list, these don't work either
customObjects.sobjectType = 'List<Custom_Object__c>';
customObjects.sobjectType = 'Custom_Object__c[]';

Can someone point me in the right direction here? Is there another way to specify the sobjectType property? Are there issues with multiple params on a remoteaction, or issues with collection-based params? 

I have a site for self-registration which calls Site.createPortalUser()  to create a new portal user if it is a new user. It works perfectly on site registration page. The problem now is that I have to capture facebook login and create portal user for facebook users. Current code has callout function to get facebook user's email, userid and username, etc. And then, pass those info to the same function used for site registration page. All parameters are correct, just don't know why Site.createPortalUser()  always give me null userId? Anyone has any idea about this?