Inconsistent accessibility

I am getting this:

Error 1 Inconsistent accessibility: parameter type 'System.Collections.Generic.List' is less accessible than method 'DetailReport.GenExcel.CreateContentRow(int, System.Collections.Generic.List, System.Collections.Generic.List)' C:\CLI\CS\DetailReport\GenExcel.cs 1161 25 DetailReport

On this:

public static Row CreateContentRow(int index, DetailRecord det, List<int> setNumber)

with the call:

Row

I know I have to make something public, but what?

Thanks,

arep

contentRow = GenExcel.CreateContentRow(index, det, setNumber);