cant get northern wall mission

I did teh defend the wall mission the other day, i cant remeber what i did after talking to simon scribe, but now when i went back i cant get the northern wall mission, he doesnt give me any at all. Can anyone help?Thanks

http://wiki.guildwars.com/wiki/Defend_the_Wall

If you have turned in this quest and received the reward, you should be at The Great Northern Wall mission. You should see a button on your party window to start the mission. After the timer runs out you'll be in the mission.

voilà!

Thanks for the quick reply. It didn't occur to me to go back to the northern wall, must be one of those days, lol