Fatal Error after updating to latest

make sure you upgrade, nd and nd_contrib as well - you'll also need to go to the plugins screen and resave that screen since we made a small API chance there.

you have 50 custom fields already ? damn, that might pose a problem indeed since properties of the custom fields have indeed changed (instead of a code key that changed to a properties key) - mmm are these fields in code or in your database ? If it's in your database, I'll write a small conversion script which you can put temporarily in ds.install to upgrade. If it's in code, you'll need to change 'code' to 'properties', ie

'code' => '<?php echo l(t("Read more"), "node/$object->nid"); ?>',
// to
'properties' => array('code' => '<?php echo l(t("Read more"), "node/$object->nid"); ?>'),

Well, to be honest, we haven't had an official alpha, beta or 1.0 release yet, so including an upgrade path is something that shouldn't be done. However, it was our fault to introduce such an API change pretty late in the process and I don't want to waste all the effort you have done so far. I'm going to post an update function here which you can use to update your code and block fields (there are still in the database right ?). I'll post this code probably today or tomorrow!

Ok here goes. Paste this code in ds.install file and run the database updates. Of course, make sure to create a backup first :)
There is one thing I can't track though. Since the latest commit, it is necessary to toggle a checkbox if you are using tokens in custom fields. You'll need to re-update those if you have used tokens. Function underneath is untested, but should work normally, let me know of course if something went wrong.

function ds_update_1() {
  foreach (module_implements('ds_api') as $module) {
    $fields = variable_get($module .'_fields', array());
    foreach ($fields as $key => $field) {

      // Block field.
      if (isset($field['block'])) {
        $fields[$key]['type'] = DS_FIELD_TYPE_CODE;
        $fields[$key]['status'] = DS_FIELD_STATUS_CUSTOM;
        $fields[$key]['properties']['block'] = $field['block'];
        $fields[$key]['properties']['render'] = $field['render'];
      }

      // Code field.
      if (isset($field['code'])) {
        $fields[$key]['type'] = DS_FIELD_TYPE_BLOCK;
        $fields[$key]['status'] = DS_FIELD_STATUS_CUSTOM;
        $fields[$key]['properties']['code'] = $field['code'];
        // Let's also add the token property.
        $fields[$key]['properties']['token'] = FALSE;
      }

      // Unset code & block key.
      unset($fields[$key]['block']);
      unset($fields[$key]['code']);
    }

    // Save.
    variable_set($module .'_fields', $fields);
  }

  $ret = array();
  return $ret;
}

Ok please wait a bit with running this - we're probably doing another API update, I'll let you know when you can run!

Ok, you may update. Make sure you have the latest version of DS, ND & ND_contrib.

function ds_update_1() {
  foreach (module_implements('ds_api') as $module) {
    $fields = variable_get($module .'_fields', array());
    foreach ($fields as $key => $field) {

      // Block field.
      if (isset($field['block'])) {
        $fields[$key]['type'] = DS_FIELD_TYPE_CODE;
        $fields[$key]['status'] = DS_FIELD_STATUS_CUSTOM;
        $fields[$key]['properties']['block'] = $field['block'];
        $fields[$key]['properties']['render'] = $field['render'];
      }

      // Code field.
      if (isset($field['code'])) {
        $fields[$key]['type'] = DS_FIELD_TYPE_BLOCK;
        $fields[$key]['status'] = DS_FIELD_STATUS_CUSTOM;
        $fields[$key]['properties']['code'] = $field['code'];
        // Let's also add the token property.
        $fields[$key]['properties']['token'] = FALSE;
        $fields[$key]['properties']['formatters'] = array('ds_eval_code' => t('Default'));
      }

      // Unset code & block key.
      unset($fields[$key]['block']);
      unset($fields[$key]['code']);
    }

    // Save.
    variable_set($module .'_fields', $fields);
  }

  $ret = array();
  return $ret;
}

After running the update should be back. It's likely you'll just have to resave some displays. Let me know if things went wrong. Marking as fixed for now.

Can you give me a dump of your variables table ? (not everything, I dont need all the rest). If I have your data, it 'll probably be easier to see what goes wrong on my screen.

Ok, fixing this offline than.

Ok ,that problems is related with build modes. So either a module defining hook_content_build_modes isn't up to date (if you coded your own hook, you'll need to update that function) or resave any custom buildmodes from the UI. Can't do much more than that.