PDO expecption error while adding class to the block with sql server "PDOException: SQLSTATE[42S22]: [Microsoft][ODBC Driver 11 for SQL
  Server][SQL Server]Invalid column name 'css_class'.: UPDATE block SET
  [css_class]=:db_update_placeholder_0 WHERE ([module] =
  :db_condition_placeholder_0) AND ([delta] =
  :db_condition_placeholder_1) ; Array ( ) in block_class_form_submit()
  (line 99 of .....\sites\all\modules\block_class\block_class.module)."


Adding class to the block using block class module. while adding class to the block throwing pdo exception error coming. Please any one resolve problem.
Instead of install one module for this, you can just use the ID for that block and create your custom css.

Example:

div#block-block-10{
    background-color: blue; 
}


I think that could solve your problem