Error while loading the data from server to core data model using restkit

i am using restkit in my project. i can sucessfully load data using the restkit and can store to data base by manually passing the loaded data to the coredata objects. Later i modified it to the restkit coredata model then i am getting the error like this. when run first time

reason = "The model used to open the store is incompatible with the one used to create the store";
 

my core data was set correctly and its working fine when i pass the data to keys manually.

i got a solution to delete the app or delete the app data from simulator file,
so i deleated the app from the simulator and again run it.this time i got the this error

 2012-05-18 17:38:45.610 MAW[85942:15203] W restkit.network:RKObjectLoader.m:281 Unable to find parser for MIME Type 'text/html'
 2012-05-18 17:38:45.612 MAW[85942:15203] W restkit.network:RKObjectLoader.m:309 Encountered unexpected response with status code: 200 (MIME Type: text/html -> URL: http://api.artworkmanager.com/v1auth?username=anuj.gakhar%40gmail.com&password=1234 -- http://api.artworkmanager.com/v1 -- http://api.artworkmanager.com/v1 -- http://api.artworkmanager.com/v1)
 2012-05-18 17:38:45.614 MAW[85942:15203] Encountered an error: Error Domain=org.restkit.RestKit.ErrorDomain Code=4 "The operation couldn't be completed. (org.restkit.RestKit.ErrorDomain error 4.)"
 

Hear is my code

// Initialize RestKit
 RKObjectManager* objectManager = [RKObjectManager objectManagerWithBaseURLString:@"http://api.artworkmanager.com/v1"];  
 objectManager.client.requestQueue.showsNetworkActivityIndicatorWhenBusy = YES;
 
 RKManagedObjectStore* objectStore = [RKManagedObjectStore objectStoreWithStoreFilename:@"MAW.sqlite"];
 
 RKManagedObjectMapping* customerMapping = [RKManagedObjectMapping mappingForClass:[Customer class]inManagedObjectStore:objectStore];
 [customerMapping mapKeyPath:@"phone" toAttribute:@"phone"];
 [customerMapping mapKeyPath:@"organization" toAttribute:@"organization"];
 [customerMapping mapKeyPath:@"siteAdministrator" toAttribute:@"siteAdministrator"];
 [customerMapping mapKeyPath:@"customerType" toAttribute:@"customerType"];
 [customerMapping mapKeyPath:@"id" toAttribute:@"id"];  
 
 RKManagedObjectMapping* articleMapping = [RKManagedObjectMapping mappingForClass:[User class]inManagedObjectStore:objectStore];
 [articleMapping mapKeyPath:@"email" toAttribute:@"email"];
 [articleMapping mapKeyPath:@"fullname" toAttribute:@"fullname"];
 [articleMapping mapKeyPath:@"id" toAttribute:@"id"];
 
 // relationship mapping
 [articleMapping mapKeyPath:@"customer" toRelationship:@"customer" withMapping:customerMapping];
 
 [[RKObjectManager sharedManager].mappingProvider addObjectMapping:articleMapping] ;
 
 [self loadData];
 

my delegate methods

-(void)loadData{
     // fetch your mapping
     RKObjectMapping *customerMapping = [[RKObjectManager sharedManager].mappingProvider objectMappingForClass:[Customer class]]; 
      //request data
      [[RKObjectManager sharedManager] loadObjectsAtResourcePath:@"auth?password=1234&username=anuj.gakhar@gmail.com/customer" objectMapping:customerMapping delegate:self];
      }
 - (void)objectLoader:(RKObjectLoader*)objectLoader didLoadObjects:(NSArray*)objects {
     RKLogInfo(@"Load collection of: %@", objects);
 
 }
 - (void)objectLoader:(RKObjectLoader*)objectLoader didFailWithError:(NSError*)error {
     NSLog(@"Encountered an error: %@", error);
 
 }
 - (void)request:(RKRequest*)request didLoadResponse: 
 (RKResponse*)response { 
     if ([request isGET]) { 
         if ([response isOK]) { 
             NSLog(@"Retrieved JSON: %@", [response bodyAsString]); 
         } 
     } else if ([request isPOST]) { 
         if ([response isJSON]) { 
             NSLog(@"Got a JSON response back from our POST!"); 
         } 
     } 
 }
 

can any one help me how can i solve this. and also suggest me in using restkit. As i am new to iphone feeling little bit difficult to with rest kit. Shall i continue with this or suggest any other alternatives i will go them. if not suggest me a good resorce to follow restkit. now i am going through this restkit in github https://github.com/RestKit/RestKit/blob/master/Docs/Object%20Mapping.md

EDIT
I have tried by running the example twiter code provided in the restkit https://github.com/RestKit/RestKit/tree/master/Examples/RKTwitterCoreData . It is also giving the same error, what might be the problem????(either ios / restkit) i have found an issue here https://github.com/RestKit/RestKit/issues/321. any ideas? thank you...

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