I'm just guessing here, but perhaps something is going wrong when AR is trying to get the list of columns for the table. Look at the log in more detail. From the point of the crash, look backward until you find a line starting with "Processing". That's the start of your request. Now look forward and see if you can identify where AR is getting the field list.
Here's an example from one of my logs (I'm using MySQL, not DB2):
Param Columns (0.004356) SHOW FIELDS FROM params
AR does this in order to figure out which field accessors to create. Your table has a "email_config_id" column, so it should create the accessor. Maybe by looking at the logs for a good request and a bad request you can see something different...