Url jumps to uncategorized

Hey all,

I’ve got a really anoying problem:

I just installed a network of WP’s. For my English section, I made some new categories and added them to a new menu.

When i’m trying to get to the post, my url is jumping eventually to the wrong url

domain.com/uncategorized/postname
instead of
domain.com/categoryname/postname

Anyone know how to fix it?