NSMutableArray addObjectsFromArray returning error

I'm having difficulty modifying a mutable array. I'd say that I am an an Intermediate level ios programmer - I'm not a complete newb, but I often forget some of the basics.

The error I'm getting is:

-[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object'

Trouble is, I declared and initialized it as an NSMutableArray. I have gone at this from a ton of different angles - I was hoping someone might give me some ideas. Here are the important highlights:

The viewcontroller looks like this:

@interface HomeScreen : UIViewController
{
...
NSMutableArray *arrayOfNewsItems;
}
...
- (void)GoAheadAndGetData;
- (void)getTweets;
- (void)renameKeysIn:(NSMutableArray*)source :(NSMutableArray*) final;
...
(some properties...)

@end

After the first viewController loads, the user clicks a button. The button is connected to a modal segue on the storyboard, so the following method runs:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([sender tag] == 1) { // if the button for loading the table is pushed:
// If there is a valid connection, go ahead and try to connect
if ([self connected]) {
[self GoAheadAndGetData];
} else { ...


...

(This all works fine, by the way)

So from there, the “GoAheadAndGetData” (which is where the array is initialized, and all data is obtained) method looks roughly like this:

- (void)GoAheadAndGetData
{
// This function starts by getting data automatically from my yahoo pipe,
// transfering it into a mutable array, then checks for other feeds

// create the string for making the api call to the yahoo pipes site
NSString* theURL = [NSString stringWithFormat:@"http://... etc..."];

// declare and assign variables necessary to generate the actual request
NSError* err = nil;
NSURLResponse* response = nil;
NSMutableURLRequest* request = [[NSMutableURLRequest alloc] init];
NSURL* URL = [NSURL URLWithString:theURL];
[request setURL:URL];
[request setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];
[request setTimeoutInterval:30];

// make the actual url request - get the data from yahoo pipes, in json
NSData* jsonData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];

// assign the entire result to a large dictionary object
NSDictionary *entireResults = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&err];

// grab the "value" field
NSDictionary *valueFieldOnly = [entireResults objectForKey:@"value"];

// ****** This is where the array in question is initialized as mutable ********
// grab the "items" field
arrayOfNewsItems = [[NSMutableArray alloc] init];
arrayOfNewsItems = [valueFieldOnly objectForKey:@"items"];
//***************************************************************

// Now check for Twitter feed settings, and merge them into the rest
NSString *settingsKey = [[NSString alloc] initWithString:@"keyTwitterState"];
BOOL toggleValue = [[NSUserDefaults standardUserDefaults] boolForKey:settingsKey];
if (toggleValue) {
NSLog(@"Called getTweets, because twitter state answered as true.");
[self getTweets];
} else {
NSLog(@"twitter state answered as false.");
}
} // end method GoAheadAndGetData

// ******* This all works, so far, also.

The following method is where the error is generated. But I find it baffling - all I'm doing is calling a mutable method on a mutable array. I won't include all of the code here, because it's long, and I'm pretty sure nothing affects anything... most of it is directly from Twitter's api documentation anyway.

- (void)getTweets
{
...
if (!responseData) {
// inspect the contents of error
NSLog(@"Error 1: %@", error);
} else {
NSError *jsonError;
NSMutableArray *timeline = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableLeaves error:&jsonError];
if (timeline) { // at this point, we have an object that we can parse
// Having retrieved the user's home Twitter timeline, we can now merge it with the newsItems.
// The keys in the timeline need to match the arrayofnewsItems, in order for them to be sorted, so call renameKeys

timeline = [self renameKeysIn:timeline];// this works fine
NSLog(@"\nReturned value from rename Keys. \n%@^^Item 1:^^\nTimeline count: %d \narrayOfNewsItems count: %d",[timeline objectAtIndex:0], [timeline count],[arrayOfNewsItems count]);

// Then we can merge them:
// ****************** THIS IS THE MAIN ERROR POINT **********

[arrayOfNewsItems addObjectsFromArray:timeline];

// ******* THIS LINE RETUNS THE Mutable method/non-mutable object error.
NSLog(@"Added the tweet array to the newsitems array. Count: %d",[arrayOfNewsItems count]);

// Then finally, sort:
NSSortDescriptor *sortByDateDescriptor = [[NSSortDescriptor alloc] initWithKey:@"pubDate" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortByDateDescriptor];
NSLog(@"\ncreated sort descriptors. Getting ready to sort the array.");
NSMutableArray *sortedArray = [NSMutableArray arrayWithArray:[arrayOfNewsItems sortedArrayUsingDescriptors:sortDescriptors]];

[arrayOfNewsItems addObjectsFromArray:sortedArray];

} else {
// inspect the contents of jsonError NSLog(@"--------------- Error: ---------------- \n\n%@", jsonError);
}
}
}];

} // if ([twitterAccounts count] > 0)
} // if (granted)
}];
} // end getTweets

And that's basically it. Sorry about the formatting. At this point, I don't feel comfortable hosting the entire project