setBackgroundImage works on simulator but real device (IOS5.1.1)

Question

I wrote some codes in viewWillAppear in order to change the background image of some buttons. It works fine in simulator. However, when I load it to a real device, it doesn't work. The device is IOS5.1.1.

Any body knows what's the problem?? Thanks!!

(void)viewWillAppear:(BOOL)animated
{

    [super viewWillAppear:animated];

    ...

    //set dataTypeSelect buttons background

    UIImage *tmpImage = [UIImage imageNamed:@"White.png"];

    [self.dataTypeSelectBut0 setBackgroundImage:tmpImage forState:UIControlStateNormal];

    [self.dataTypeSelectBut1 setBackgroundImage:tmpImage forState:UIControlStateNormal];

    [self.dataTypeSelectBut2 setBackgroundImage:tmpImage forState:UIControlStateNormal];

    tmpImage = [UIImage imageNamed:@"Cyan.png"];

    iTDLAppDelegate *tmpAppDelegate = (iTDLAppDelegate *)[[UIApplication sharedApplication] delegate];

    switch(tmpAppDelegate.viewingDataType)
    {
        case EnumDataType_HkHorse:
            [self.dataTypeSelectBut0 setBackgroundImage:tmpImage forState:UIControlStateNormal];
            break;
        case EnumDataType_S1:
            [self.dataTypeSelectBut1 setBackgroundImage:tmpImage forState:UIControlStateNormal];
            break;
        case EnumDataType_S2:
            [self.dataTypeSelectBut2 setBackgroundImage:tmpImage forState:UIControlStateNormal];
            break;
    }

    ...

}

Answer 1

I have pinpointed it was caused by the image filenames.

The file names are "White.PNG" and "Cyan.PNG".
My codes are as follows

UIImage *tmpImage = [UIImage imageNamed:@"White.png"];
UIImage *tmpImage = [UIImage imageNamed:@"Cyan.png"];

They work fine in simulator but real device.
I found the returned value of tmpImage is null in real device.

Now I changed them to

UIImage *tmpImage = [UIImage imageNamed:@"White.PNG"];
UIImage *tmpImage = [UIImage imageNamed:@"Cyan.PNG"];

They work fine for both now. :)