[__NSCFNumber length]: unrecognized selector sent to instance 0x6d21350 - iphone

Question

What could this error mean?
[__NSCFNumber length]: unrecognized selector sent to instance 0x6d21350
Here is my code:
NSString *urlString = #"http://api.twitter.com/1/statuses/update.json";
NSURL *url = [NSURL URLWithString:urlString];
NSMutableDictionary *params = [[NSMutableDictionary alloc] init];
[params setObject:status forKey:#"status"];
[params setObject:replyToID forKey:#"in_reply_to_status_id"];
[params setObject:#"1" forKey:#"include_entities"];
// Build the request with our parameter
TWRequest *request = [[TWRequest alloc] initWithURL:url parameters:params requestMethod:TWRequestMethodPOST];
// Attach the account object to this request
[request setAccount:twitterAccount];
[request performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error) {
if (!responseData) {
// inspect the contents of error
NSLog(#"%#", [error localizedDescription]);
self.alert = [[UIAlertView alloc] initWithTitle:#"HTTP error" message:#"I could not connect to the Twitter API." delegate:self cancelButtonTitle:nil otherButtonTitles:#"OK", nil];
[self.alert show];
[self.replyDelegate replyRequestSuccessful:NO];
}
else {
/*NSString *responseDataAsString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
NSLog(responseDataAsString);*/
NSError *error;
NSArray *replyResponse = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableLeaves error:&error];
if (!replyResponse) {
NSLog(#"%#", [error localizedDescription]);
self.alert = [[UIAlertView alloc] initWithTitle:#"JSON error" message:#"I could not parse the JSON response from the Twitter API." delegate:self cancelButtonTitle:nil otherButtonTitles:#"OK", nil];
[self.alert show];
[self.replyDelegate replyRequestSuccessful:NO];
}
else {
[self.replyDelegate replyRequestSuccessful:YES];
}
}
}];
I tried debuggin, and it dies once it enters the performRequestWithHandler. It goes the else block and dies with the error above.

Answer 1

It means that you are passing an NSNumber where the called code expects an NSString or some other object that has a length method. You can tell Xcode to break on exceptions so that you see where exactly the length method gets called.

Answer 2

Specifically this line of code:
[params setObject:replyToID forKey:#"in_reply_to_status_id"];
the replyToID is not a String or has a method length. If you don't have this, or if you convert the replyToID to a String before setting it in params it should work.