NSNotification arrived with broken object

i'm posting notification in this manner:

...
IVSession *newSession = [[[IVSession alloc] initWithDictionary:propertyDict] autorelease];     

NSDictionary *notifParams = [NSDictionary dictionaryWithObject:newSession  forKey:@"session"];        
NSNotification *newSessionNotif = [NSNotification notificationWithName:IVNewSessionNotificaiton object:se开发者_StackOverflow中文版lf userInfo:notifParams]; 
...

IVSession interface:

@interface IVSession : IVMappableObject {
    NSString *_ssid;
    NSNumber *_uid;    
}

@property (nonatomic,retain) NSString *sessionID;
@property (nonatomic,retain) NSNumber *userID;

and init method:

- (id)initWithDictionary:(NSDictionary*)dict
{
    if ((self = [super init]))
    {
        NSDictionary *mapping = [self elementToPropertyMappings];
        for (NSString *key in mapping)
            [self setValue:[dict objectForKey:key] forKey:[mapping objectForKey:key]];
    }    
    return self;
}

but at the method, called for this notification, i'm receiving broken newSession object - its properties ssid and uid are invalid summaries:

-(void)didOpenSession:(NSNotification *)newSession
{
    if (receivedSession)
        [receivedSession release];
    receivedSession =  [[newSession userInfo] objectForKey:@"session"];
} 

where is my fault?

code looks ok to me... have you verified that the IVSession object contains what you expect it to, after assembling things, but prior to posting the notification?