Urls ending with, say ...-20 or any other digits will generate an error

I am trying to add in my language a category for BMW/seria-3(3 series) but i get an error when i am trying to add it : "Urls ending with, say ...-20 or any other digits will generate an error". I really can't create the URL in this form www.website.com/auto/bmw/seria-3 ?

Thanks!

You can't create urls which ends with the dash then number, such urls flynax uses for the detailed listing pages, please type it differently - maybe 3-series

I have the same problem when i am trying to edit a listing category.