Code that worked before gets not set to an instance

Question

I am getting this in code that has worked before in a couple of other programs.  Here is the error.

Maybe it is the data coming in.  I am only moving one field to test.
 

System.NullReferenceException: Object reference not set to an instance of an object.

   at Evolent_PHCS.GenXML.DataRows(SheetData sd, String sheetName, List`1 classList, List`1 setNumber, Worksheet ws) in c:\Evolent-PHCS\GenXML.cs:line 383

   at Evolent_PHCS.GenXML.AddWSdata_PHCS(Worksheet& ws, SheetData& sd, String sheetName, List`1 header, List`1 listData, List`1 setNumber) in c:\Evolent-PHCS\GenXML.cs:line 89

   at Evolent_PHCS.GenXML.Build_PHCS(String path, List`1 header, List`1 PHCS_List, List`1 Multiplan_List, List`1 setNumber) in c:\Evolent-PHCS\GenXML.cs:line 53

   at Evolent_PHCS.Program.ExtractData() in c:\Evolent-PHCS\Program.cs:line 229

   at Evolent_PHCS.Program.Main(String[] args) in c:\Evolent-PHCS\Program.cs:line 79

Thanks ahead of time,

arep