Just to elaborate a little bit… The Excel Buffer table is used mostly to build data in a temporary record variable, and then use one of its functions to create an Excel sheet from that data. Because it is mostly used as a temporary record variable, you won’t see any data when you run the table from the object designer. The primary key of the table is “Row No.,Column No.”, so there can only be 1 record per combination of “Row No.” and “Column No.”. The error you are getting tells you that the process that you are running is trying to insert a record with certain primary key values, and that this record already exists. You’re going to have to debug the process to see where it breaks and what it is trying to do at that point.
It might be that your date range filter has something to do with how the process calculates the row and column numbers, but in itself the date has nothing to do with the error message.