Azure Mobile Service Offline Data Sync - The item provided was not valid

I am using Azure Mobile Service as a backend for an iOS app. I have set up everything to work with offline sync which allows me to view, add, or modify data even when there is no network connection. I am now into testing and I run into an error: "The item provided was not valid" when I try to synchronize data.

Here's what I am doing:

I add a new athlete to the syncTableWithName:@"Athlete" with this:

NSDictionary *newItem = @{@"firstname": @"Charles", @"lastname": @"Lambert", @"laterality" : @"Orthodox"};

        [self.athletesService addItem:newItem completion:^{
            NSLog(@"New athlete added");
        }];

Here's the addItem function:

-(void)addItem:(NSDictionary *)item completion:(CompletionBlock)completion
{
    // Insert the item into the Athlete table
    [self.syncTable insert:item completion:^(NSDictionary *result, NSError *error)
     {
         [self logErrorIfNotNil:error];

         // Let the caller know that we finished
         dispatch_async(dispatch_get_main_queue(), ^{
             completion();
         });
     }];
}

For now everything is fine and the item is in the syncTable. The problem is when I try to synchronize with the Azure Mobile Service. Here's the syncData function I am calling:

-(void)syncData:(CompletionBlock)completion
{   
    // push all changes in the sync context, then pull new data
    [self.client.syncContext pushWithCompletion:^(NSError *error) {
        [self logErrorIfNotNil:error];
        [self pullData:completion];
    }];
}

The pushWithCompletion gets me the error: "The item provided was not valid." and same for the pullData function that gets called after:

-(void)pullData:(CompletionBlock)completion
{
    MSQuery *query = [self.syncTable query];

    // Pulls data from the remote server into the local table.
    // We're pulling all items and filtering in the view
    // query ID is used for incremental sync
    [self.syncTable pullWithQuery:query queryId:@"allAthletes" completion:^(NSError *error) {
        [self logErrorIfNotNil:error];

        // Let the caller know that we finished
        dispatch_async(dispatch_get_main_queue(), ^{
            completion();
        });

    }];
}

I have tried inserting directly in the MSTable and that works fine. It's really when I am using the MSSyncTable that I run into this error. Although when I insert data manually in my database and that I synchronize my context I can fetch data and display within my UITableView.

Lookin forward to see what you guys think about this. Thanks a lot!

I just edited my question thanks to @phillipv. When I add an item using NSDictionary just like I did I run into the error "The item provided was not valid". So I tried adding an item by first inserting it to my managedObjectContext and then calling:

NSDictionary *dict = [MSCoreDataStore  tableItemFromManagedObject:newAthlete];

I then I get the error when I try to sync: "The item provided did not have a valid id."

I feel like I am experiencing a circle.. :S