NSDateFormatter returning nil in OS 4.0

I found out it works if you do it this way (see below). The key is using the method:
- [NSDateFormatter getObjectValue:forString:range:error:]

instead of

-[NSDateFormatter dateFromString]

The complete code:

+ (NSDate *)parseRFC3339Date:(NSString *)dateString 
{
    NSDateFormatter *rfc3339TimestampFormatterWithTimeZone = [[NSDateFormatter alloc] init];
    [rfc3339TimestampFormatterWithTimeZone setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];
    [rfc3339TimestampFormatterWithTimeZone setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];

    NSDate *theDate = nil;
    NSError *error = nil; 
    if (![rfc3339TimestampFormatterWithTimeZone getObjectValue:&theDate forString:dateString range:nil error:&error]) {
        NSLog(@"Date '%@' could not be parsed: %@", dateString, error);
    }

    [rfc3339TimestampFormatterWithTimeZone release];
    return theDate;
}