Hello,
when I enable Permalinks with Elena theme , it don't work and appear error 404 but it work well with others theme .

@mphker
Please try this.
Go to file:
oc-content/themes/elena/functions.php

Find code:
// IF CATEGORY IS 0, REPLACE WITH EMPTY
if(Params::getParam('sCategory') == 0) {
  if(method_exists('Params', 'unsetParam')) {
    Params::unsetParam('sCategory');
  } else {
    Params::setParam('sCategory', '');
  }
}

Remove it.

solved , thanks