Q:

CoreData could not fulfill a fault when adding new attribute

I am receiving a "CoreData could not fulfill a fault for ..." error message when trying to access a new attribute in a new data model.  If I work with new data I'm ok, but when I attempt to read existing data I get the error.  Do I need to handle the entity differently myself if the attribute isn't in my original data?  I was under the impression that Core Data could handle this for me.  My new attribute is marked as optional with a default value. 
I have created a new .xcdatamodel (and set it to be the current version) and updated my NSPersistentStoreCoordinator initialization to take advantage of the lightweight migration as follows:
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:      
         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
         [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

NSError *error = nil;
persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] 
          initWithManagedObjectModel:[self managedObjectModel]];

if (![ persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType 
            configuration:nil URL:storeUrl options:options error:&error]) 
{
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
 }    

Any help is appreciated. 
UPDATE:
After more digging I've updated my managedObjectModel to:
- (NSManagedObjectModel *)managedObjectModel {

    if (managedObjectModel ! = nil) {
        return managedObjectModel;
    }
    //managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    

    NSString *path = [[NSBundle mainBundle] pathForResource:@"< MyModel >" ofType:@"momd"];
    NSURL *momURL = [NSURL fileURLWithPath:path];
    managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];

    return managedObjectModel;
}

This still hasn't resolved my problems.  I've clean and rebuilt, but still no love.  

A:

Turns out that there was no problem with the versioning.  I had some rather (too) complex logic which removed my object from the model and then I later tried to access it. 
+1 to Marcus for the additional debugging pointers, they will no doubt come in handy at some point. 