Symptom:

Receiving this error within your DNN installation

Purge Schedule History Schedule history purge failed.System.Data.SqlClient.SqlException (0x80131904): Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

Resolution:

This condition can occur when the ScheduleHistory table is too large for it to be cleaned within the 30 second timeout. The solution is to manually purge the table by using the SQL "truncate table" command.