Ok, I have done that but nothing. Then I've tried to delete the added type e then rewrote them again. After that all has gone ok. I can't understand what could be the problem but now all work ok.
Another question: is it normal that, after changing document type, i'm not able to change it again?
For example, i have set a document as Article. Then, if i click on change type again, the combobox in the popup is empty.