Adding a row item from one datatable to another


I am attempting to add a row item from the data table ‘ReportDT’ to another data table ‘WIDT’ whenever and item from a certain column in ReportDT matches another item from a certain column in WIDT. If there is a match I am trying to take certain values from ReportDT and place them under certain columns within WIDT. I am using the below expression but I am getting the following error - Assign: Index was outside the bounds of the array. Would anyone know where I am gong wrong here?