Add Hyperlinks to Excel Through C#

Question

I have been running this syntax in VBA which works exactly as it should

Function AH()
Dim lr As Long, i As Long
Dim sSheet As String
Dim WS As Worksheet
Set WS = ActiveSheet
lr = Cells(Rows.Count, 2).End(xlUp).Row
For i = 2 To lr
  If WS.Cells(i, 2).Value Like "*,*" Or WS.Cells(i, 2).Value Like "*'*" Or WS.Cells(i, 2).Value Like "*&*" Or WS.Cells(i, 2).Value Like "*-*" Or WS.Cells(i, 2).Value Like "*.*" Then
    ActiveSheet.Hyperlinks.Add Anchor:=WS.Cells(i, 15), Address:="", SubAddress:="'" & WS.Cells(i, 2).Value & "'!A1", TextToDisplay:=CStr(WS.Cells(i, 15))
  Else
    ActiveSheet.Hyperlinks.Add Anchor:=WS.Cells(i, 15), Address:="", SubAddress:=WS.Cells(i, 2).Value & "!A1", TextToDisplay:=CStr(WS.Cells(i, 15))
  End If
Next i
WS.Activate
End Function

Now I just tried to port this to C# and it does not throw any errors, and it seems to function exactly as it shoudl, however whenever I try to click one of the links I get this error 'reference is not valid'

What is incorrect in this syntax?

public void AddHyperlinksToTotalWorksheet()
{
	long lr, i;
	string cellVal;
	Excel.Worksheet WS = xlApp.ActiveWorkbook.ActiveSheet;
	lr = WS.Cells[WS.Rows.Count, 2].End(Excel.XlDirection.xlUp).Row;
	for (i = 2; i <= lr; i++)
	{
		cellVal = WS.Cells[i, 2].Value;
		Excel.Range rangeToHoldHyperlink = WS.Range["O" + i];
		if (cellVal == "*,*" || cellVal == "*'*" || cellVal == "*&*" || cellVal == "*-*" || cellVal == "*.*")
			xlApp.ActiveSheet.Hyperlinks.Add(rangeToHoldHyperlink, "", "'" + cellVal + "!A1", "");
		else
			xlApp.ActiveSheet.Hyperlinks.Add(rangeToHoldHyperlink, "", cellVal + "!A1", "");
	}
}