Invalid Argument exception when using setText on UILabel

Im going crazy trying to debug a problem, where I get an exception

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString setText:]: unrecognized selector sent to instance 0x5799c90'

the code that is throwing it is:

- (void)request:(ASIHTTPRequest *)request didReceiveBytes:(long long)bytes
{

    for(int index=0;index<[pendingDownloadsArray count];index++)
    {
        if ([request isE开发者_StackOverflow中文版qual:[[pendingDownloadsArray objectAtIndex:index]objectForKey:@"request"]])
        {
            NSNumber *x = [[pendingDownloadsArray objectAtIndex:index] objectForKey:@"completed"];

            float newCompleted = [x floatValue]+(float)bytes;
//          x+=(float)bytes;
                        NSLog(@"Completed: %fKb",newCompleted/1024);
            x = [NSNumber numberWithFloat:newCompleted];

            [[pendingDownloadsArray objectAtIndex:index] setObject:x forKey:@"completed"];
            float progress = newCompleted / (float)request.contentLength;

            //Dont try to get cell if the table is showing something else.
            if(self.selectedSegment ==0)
            {
                DownloadsCustomCell *cell =(DownloadsCustomCell*) [downloadsTableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:index inSection:0]];
                [cell.downloadProgressView setProgress:progress];
                NSString *progressLabelText = [NSString stringWithFormat:@"%.2f percent (%.2fKb / %.2fKb)",progress*100,
                                           newCompleted/1024,((float)request.contentLength/1024)];
                NSLog(@"%@",progressLabelText);
                UILabel *label = cell.downloadProgressLabel;
                label.text = progressLabelText;
            }

        }

    }
}

its throwing the exception on the last line. (i did not have the unnecessary 'label' at first... so its existence is a mark of how confused i am. either problem is something I didnt know, or im doing something incredibly stupid that I am not able to spot. Can you please help me assign that NSString to that UILabel? (PS: i checked, downloadsProgressLabel IS A UILABEL.)

Option 1 - The problem is that the label was deallocated. cell.downloadProgressLabel points to bad memory, which happens to be a string sometimes, you should get different errors when executing that code.

Option 2 - you're creating downloadProgressLabel as a string instead of a uilabel, or you're doing cell.downloadProgressLabel = [some string object]; somewhere in the code by mistake, although that should give a warning :)

I have doubt over below line, Check the type of downloadProgressLabel , it could be NSString declared in your cell class,

Use below code.

if ([cell.downloadProgressLabel isKindOfClass:[UILabel class]])
{
    UILabel *label = cell.downloadProgressLabel;
    label.text = progressLabelText;
}