Permalink %postname% Question

Hi,

I have a wordpress blog and i am currently trying to change the permalinks to %postname% So i put this code in the ‘Custom Structure’ box and click save changes. So it says it has updated it successfully but when i try and view a post on my blog i get ‘page not found’ Does anyone know why this is happening and how i can resolve this issue please? When i switch back to default permalinks then i can view all my posts fine. I am currently running my blog off Godaddy hosting.

Thanks in advanced!