so earlier i was in the strip and got a mission from the NCR ambassoder and when i completed the mission and tried to go back into the strip its says its locked and i need a key does anyone know how to fix the problem

I'ts a bug, you will have to reload an older Save

Sorry but it is the only solution for now, that or find another way to enter the Strip using other road or medium.

dang i overright my saves anyone know if there is a different way into the strip besides freeside

Mojave outpost by New Vegas has a Monorail you can use if you have an NCR uniform.

http://www.gamesas.com/index.php?/topic/1123721-free-entry-into-the-strip/