This error is thrown when a user attempts to save the seating layout configuration of an event. When the user fills in the number of rows, tables, and seats they receive the error after clicking the Save button.
This error is caused by event sub-sections being added that already exist. Running the following query will identify if there are duplicate subsections.
select NAME from dbo.EVENTSEATINGSUBSECTION group by NAME, EVENTSEATINGSECTIONID having count(NAME) > 1
If results are return, you will need to rename the duplicate sub-sections or delete them.