File write with [NSBundle mainBundle] fails

I am trying to take content from one file and write it into another. I am reading fine, but I am not able to write it into another file.

I have a database of words. I want to separate the words into different files based on the number of letters. All four letter words go into one file, and so on. I added a txt file called "4letter" into my resources and the following is my code:

NSError *error;

//READ
NSString *dbFile = [[NSBundle mainBundle] pathForResource:@"words" ofType:@"txt"];
NSString *test = [NSString stringWithContentsOfFile:dbFile encoding:NSUTF8StringEncoding error:&error];

//convert from string to array
NSArray *lines = [test componentsSeparatedByString:@"\n"]; 

NSFileHandle *logFile = nil;
logFile = [NSFileHandle fileHandleForWritingAtPath:[[NSBundle mainBundle] pathForResource:@"4letter" ofType:@"txt"]];

//Test if write works
for (int i=0; i<5; i++) 
{
    NSString *randomAnagram = [[lines objectAtIndex:i] lowercaseString];
    [logFile writeData: [randomAnagram dataUsingEncoding: NSNEXTSTEPStringEncoding]];
}