The problem was, that some of the images i had to edit, had more then 1 path. And sometimes, some of that existing paths were already named the way i had to name the 1. Path.
However, when i was using [p] instead of [0] (wich i did first), i had to accept the name change in those cases by pressing enter and received an error message after.
(path name was already given)
After i used "0" instead of "p" it worked.
But like i already said, i got like 1% clue of what i actually did here. Im just glad it worked somehow. 
If you are enthusiastic enough to teach me why i had that problem, i'm willing to learn.
Thank you!