permalinks structure change

what do you mean by that . Chnage the whole permalink structure ?

I do have this problem too as andax. If I change the permalinks as “post name”, wordpress changes me all the permalinks for the previous articles, that means I’ll have all 404 pages not found.

Instead, if I select “custom structure”, leaving what I have now “/blog//%year%/%monthnum%/%day%/%postname%/”, wordpress doesn’t leave me the option “custom structure” activated, because it recognizes that it is the same that the “day and name” and so it switches automatically to the previous selection I had after saving.

so, is it mandatory?