Can't figure out this NSDateComponents error

I have the following statements:

NSDate *Today = [NSDate dateWithTimeIntervalSinceNow:0];
NSDate  *cDate =  [Lines objectAtIndex:(NSUInteger) 0];
NSLog(@"cDate: %@  Today: %@", cDate, Today); 
NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger desiredComponents = (NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit);
NSDateComponents *secondComponents = [calendar components:desiredComponents fromDate:Today];
NSDateComponents *firstComponents  = [calendar components:desiredComponents fromDate:cDate]; 

NSLog statement prints:cD开发者_StackOverflow中文版ate: 2011-08-16 18:35:29 +0000 Today: 2011-08-17 15:53:19 +0000

The last statement (firstComponents) which is very similar to the previous statement(secondComponents) crashes with the following error: unrecognized selector sent to instance

Thanks for any help.

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Check if cDate really is an instance of NSDate. It could also be for example an NSString instance with the value "2011-08-16 18:35:29 +0000".