When I upgraded to 2nd dan,in the game it said I was second dan,but in the forums or the shop,when I check my achievement's,I still don't have the achievement 2nd dan.

Just wait some achievements appear the next day.

You have to wait a little bit. I think.

or just refresh it a couple times and wait for it to register.

chill SnipersFan xD
you must wait because toribash.com need a little bit time!
by me it was the same from 9 th dan to 10 th dan ;P

I think the forum server updates every hour.

The achievements take time to update. It can be from a day, to a week, to a month. You still aquired the achievement, it just takes time to show.

It doesn't take a month. =|

Give it 24 hours or so.