Question

NSString *path = [[NSBundle mainBundle] bundlePath];
NSString *finalPath = [path stringByAppendingPathComponent:@"HighScore.plist"];
NSMutableArray* plistDict = [[NSMutableArray alloc]
                             initWithContentsOfFile:finalPath];   
[plistDict addObject:[highScoreLabel  text]];
NSArray *regArray =  [NSMutableArray arrayWithArray:plistDict];
[regArray writeToFile:@"HighScore.plist" atomically: YES]; 

Answer 1

Does the file exist and contains valid data?

See Apple’s documentation about NSMutableArray initWithContentsOfFile::

Return Value

An array initialized to contain the contents of the file specified by aPath or nil if the file can’t be opened or the contents of the file can’t be parsed into an array. The returned object might be different than the original receiver.

Discussion

The array representation in the file identified by aPath must contain only property list objects (NSString, NSData, NSArray, or NSDictionary objects). The objects contained by this array are immutable, even if the array is mutable.

If initWithContentsOfFile: returns nil, it’s clear that the rest of the code won’t work either.