NSMutableArray as a Property - addObject: is an unrecognized selector?

In my header file I declare this property:

Code:

@property (readwrite, retain) NSMutableArray *clippings;

The synthesizer is in the main file:

Code:

@synthesize clippings;

And here's the code where it crashes:

Code:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    NSString *clipPath = [[NSBundle mainBundle] pathForResource:@"Clippings" ofType:@"txt"];
    NSString *clipString = [NSString stringWithContentsOfFile:clipPath encoding:NSUTF16BigEndianStringEncoding error:NULL];
    self.clippings = (NSMutableArray *)[clipString componentsSeparatedByString:@"\n"];
    
    if (![self.clippings containsObject:[UIPasteboard generalPasteboard].string])
    {
        [color="RED"][self.clippings addObject:[UIPasteboard generalPasteboard].string];[/color]
    }
}

The line in red gets highlighted and in the crash log it says:

I declared it as a NSMutableArray, I set up the property to be read-write, and I cast it as a mutable array when I set it. I can't imagine what else I could do to try to make it accept [addObject] besides having an inelegant work around of copying my array's contents into a new array with a new object added in.

Many thanks to anyone who can offer some help with this.