My dateFromString is not working and i'm not sure why

```
NSString *purchase = @"2011-09-30 17:47:57";
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"yyyy-MM-dd hh:mm:ss"];
NSDate *date = [dateFormat dateFromString:purchase];

```

date is 'invalid CFStringRef'

See anything i might be overlooking?