This comment closer to your, just open phpmyadmin, locate your database on left side, click SQL button on the top, and paste SQL code from comment:
UPDATE variable SET value = 'i:1000;' WHERE name = 'drupal_weight_select_max';
Then you should clear your cache, for this run clearing cache in Drupal in Performance section or do manually:
Locate Cache table, click Operations, and click on Empty the table (TRUNCATE) link.
But you should be sure that this variable exists in variable table. For this, click on Variable table, click Search button on the top, enter drupal_weight_select_max on Value for Name row and click Go.
If table exists, running SQL or updating located row will enough (clear Cache of course), otherwise click Insert and enter values that provided in comment: drupal_weight_select_max, i:1000;
For inserting, clearing cache doesn't need.