ImpressPages CMS logs errors and important events. All messages are accessible in administration panel on tab Administrator -> Log.

By default all messages are stored for 30 days. Follow these steps to change this value:

• Open administration panel
• Go to Developer -> Modules config tab
• Choose Log in the left panel
• Press yellow icon in parameters line on the right 
• Change "Log size in days" value to any number you like
• New property will take affect on next cron job.