Not saving changes on menu

Hi everyone

A few weeks ago i got asigned the duty to mantain and publish my job’s webpage. I had never used drupal before, so i’m learning with each change they ask.

Just recently have upgraded it to version 7.51 from 7.41, and since then, i cant make changes on menus. It lets me activate/deactivate existing links, and delete them, but each time i change the path of the link, or create a new one, nothing happens, or it throws a 500 error.

dont know if its because of the upgrade, or if i have done something wrong i haven’t noticed (cause i was able to do it 2 weeks ago)

Thanks beforehand for the help.

Drupal version: