instead of rendering the 20 frames of the animation it only renders the first one and stops as if it was a "render frame" and not a "render Animation"(ctrl F12) process
this only happens in this project file and new projects render just fine
i reduced the blend file to reproduce the error. thanks a lot.
i had copied the user preferences from my older computer in which the render directory in the settings was Drive F:/ . and this partition doesnt exist in my new computer. changing the output directory from preferences and "output properties" tab solved the issue. thank you everyone your comments helped a lot.