Create Range List Code For Data Validation

I am using following code to apply data validation list. However this code gives error Intermittently. The error message is 'Application defined or Object defined error'. Also this code looks little cumber some. Will really apprciate if any one can put some ligh on why is this error appearing sometimes. Do I need to change something in the code or add few extra lines. I feel following points will be necessary when you check my code

1. The data of validation list is stored under the column heading 'Reported_By_List'
2. Validation is applied on the range under the column heading 'Reported Through'
3. Start and last Cell Address Of the cells of the column in which data of validation list is
stored are extracted into the variables 'StartCellAddress1' & 'LastCellAddress1 '
4. Start and last Cell Address Of the cells of the column on which data validation will be
applied are stored are extracted into the variables 'StartCellAddress2' &
'LastCellAddres2'

Sub Validation1()

Dim wsName As String
Dim RValue As String
Dim WorkBookName As String
Dim StartRow As Integer
Dim StartColumn As Integer
Dim LastRow As Integer
Dim CellAddress As String
Dim ColumnAddress As String
Application. ScreenUpdating = False
WorkBookName = ThisWorkbook.Name
wsName = ActiveSheet.Name...........