AsyncException. Any problem with an asynchronous operation, such as failing to enqueue an asynchronous call. CalloutException. Any problem with a Web service operation, such as failing to make a callout to an external system. DmlException. Any problem with a DML statement, such as an insert statement missing a required field on a record. This procedure is similar to the previous one with the exception that it runs through all files within a single directory (excluding subdirectories – for that scroll to next procedure). ... # Loop through files and replace "search" . Next, open the CSV file for writing by calling the open() function. In plain English, this is a text file that.