exec functions not working from linux daemon

Question

I have been writing a linux daemon which listens on TCP/IP for a request and launches an application on receiving that request. My problem is when I run this daemon from command prompt or IDE (eclipse 3.7) everything works fine and my executable launches. But when i use
sudo service <myservicename> start It will receive request on socket but its not launching that executable.

here is the standard code I am using for daemonizing the process /// Linux Daemon related stuff

/// Create the lock file as the current user 
int lfp = open( "/var/lock/subsys/LauncherService", O_RDWR|O_CREAT, 0640);
if ( lfp < 0 ) 
{
    LOG_ERROR ("Unable to open lockfile");
    LOG_ERROR ( strerror(errno) );
}

/// All
/// Our process ID and Session ID
pid_t pid, sid;

/// Fork off the parent process
pid = fork();
if (pid < 0) {
       exit(EXIT_FAILURE);
}

/// If we got a good PID, then
///  we can exit the parent process.
if (pid > 0)
{
    exit(EXIT_SUCCESS);
}

/// Change the file mode mask
umask(0);

/// Create a new SID for the child process
sid = setsid();
if (sid < 0)
{
    LOG_ERROR ("Error Setting sid");
    exit(EXIT_FAILURE);
}
LOG_INFO ("sid set");

/// Change the current working directory
if ( (chdir("/usr/local/<mylocaldir>/bin")) < 0 )
{
       LOG_ERROR ("Error changing Directory");
       exit(EXIT_FAILURE);
}
LOG_INFO ("chdir successful");

/* Close out the standard file descriptors */
close(STDIN_FILENO);
close(STDOUT_FILENO);
close(STDERR_FILENO);

here is function in which i am launching my binary which needs to be launched. This function is called in forked child process.

std::string configFile = "/usr/local/<mydir>/config/Settings.config";
std::string binary = "<binaryname>";
std::string path ="/usr/local/<mydir>/bin/<binaryname>";

//char *argv[] = { "<binaryname>", "/usr/local/<mydir>/config/Settings.config", (char *)0 };

LOG_INFO("Calling Process" );
if ( execlp( path.c_str(), binary.c_str(), configFile.c_str(), (char *)0 ) == -1 )
//if ( execv("/usr/local/<mydir>/bin/<binaryname>", argv) == -1 )
//if ( execvp("/usr/local/<mydir>/bin/<binaryname>", argv) == -1 )
{
    LOG_ERROR("System call failed !!")
    std::string errString = strerror(errno);
    LOG_ERROR (errString );
}
else
{        
    LOG_INFO("System call successful");
}

Answer 1

So after discussion with Casey I investigated more into my called program and I found that my program indeed is getting called. Also I found out that environment variables are not the issue child process is taking environment from parent itself. I am creating QApplication (qt gui application) in my main program. Its some issue with that and linux system daemon. I will try to figure that out and will ask separate question if needed.

Edit: Final Solution It was a qt GUI application which was not able to connect to XServer. I had to changes suggested by Casey and given in this post Cannot connect to X server :0.0 with a Qt application

after that it started launching.