Sorry Kiddo ...

Theres plenty of perks to being Madonnas daughter -- but apparently, even those perks have their limits -- like automatic entry into fashion shows.

Lourdes Leon and a friend thought theyd be able to stroll right into the Marc Jacobs Runway show Thursday night without issue ... but that wasnt the case. Check out the video, paps swarm Lourdes on her way into the Park Avenue Armory.

The two try to walk past security, but the guards arent havin it ... blocking the entry and refusing to let them inside.

At one point, even the paparazzi chant "Let her in!" as Lourdes and her friend crack up, but the security guards dont crack.

Finally, after a few phone calls, Lourdes and her friend give up -- getting back into their waiting SUV and leaving. Unclear where they were headed, but hopefully they had a reservation.