Taking over a spread sheet with a macro not working, (I'm just a novice with VBA)

Debug error points to:
BuildPlan(Worksheets(SourceWorksheet).Cells(j, "A"), Worksheets(SourceWorksheet).Cells(j, "E"), Worksheets(SourceWorksheet).Cells(j, "F")) = Worksheets(SourceWorksheet).Cells(j, "K")

Sub is below:

Sub UpdateMonthForecast()

Dim Month As Integer
Dim Year As Integer
Dim PartRow As Integer
Dim SourceRow As Integer
Dim SourceWorksheet As String
Dim Column(1000) As String
Dim ColumnCount As Integer
Dim j As Long
Dim i As Integer
Dim Msg As String

Dim BuildPlan(5000000 To 5200000, 2014 To 2016, 1 To 12) As Long
Dim PartNumbers(5000000 To 5200000) As String

Column(0) = "A"
Column(1) = "B"
Column(2) = "C"
Column(3) = "D"
Column(4) = "E"
Column(5) = "F"
Column(6) = "G"
Column(7) = "H"
Column(8) = "I"
Column(9) = "J"
Column(10) = "K"
Column(11) = "L"
Column(12) = "M"
Column(13) = "N"
Column(14) = "O"
Column(15) = "P"
Column(16) = "Q"
Column(17) = "R"
Column(18) = "S"
Column(19) = "T"
Column(20) = "U"
Column(21) = "V"
Column(22) = "W"
Column(23) = "X"
Column(24) = "Y"
Column(25) = "Z"

' Define Column Array

ColumnCount = 26
For j = 0 To 10
For i = 0 To 25
Column(ColumnCount) = Column(j) + Column(i)
ColumnCount = ColumnCount + 1
Next i
Next j

Application.Calculation = xlCalculationManual
Application.Cursor = xlWait

j = Range("Forecast_MonthPartList").Rows(1).Row
Do While Worksheets("Forecast").Cells(j, "C") <> ""
If Worksheets("Forecast").Cells(j, "C").Interior.ColorIndex = xlNone Then
Worksheets("Forecast").Range("D" & j, "AA" & j).Value = ""
End If
j = j + 1
Loop

' Read Forecast from SupplyDemand data sheet

SourceWorksheet = "T_Rp1_SupplyDemandData_byMonth"

j = 2
Do While Worksheets(SourceWorksheet).Cells(j, "A") <> ""
BuildPlan(Worksheets(SourceWorksheet).Cells(j, "A"), Worksheets(SourceWorksheet).Cells(j, "E"), Worksheets(SourceWorksheet).Cells(j, "F")) = Worksheets(SourceWorksheet).Cells(j, "K")
j = j + 1
Loop

' Populate Forecast worksheet

For PartRow = Range("Forecast_MonthPartList").Rows(1).Row To Range("Forecast_MonthPartList").Rows(Range("Forecast_MonthPartList").Rows.Count).Row
For Year = 2014 To 2016
For Month = 1 To 12
If Worksheets("Forecast").Cells(PartRow, "C").Interior.ColorIndex = xlNone Then
If Year = 2014 Then
If Worksheets("Forecast").Cells(PartRow, "C").Value = 5122053 Then
Worksheets("Forecast").Cells(PartRow, Column(Month + 2)).Value = "=4*" & BuildPlan(Worksheets("Forecast").Cells(PartRow, "C").Value, Year, Month)
Else
Worksheets("Forecast").Cells(PartRow, Column(Month + 2)).Value = BuildPlan(Worksheets("Forecast").Cells(PartRow, "C").Value, Year, Month)
End If
Else
If Worksheets("Forecast").Cells(PartRow, "C").Value = 5122053 Then
Worksheets("Forecast").Cells(PartRow, Column(Month + 14)).Value = "=4*" & BuildPlan(Worksheets("Forecast").Cells(PartRow, "C").Value, Year, Month)
Else
Worksheets("Forecast").Cells(PartRow, Column(Month + 14)).Value = BuildPlan(Worksheets("Forecast").Cells(PartRow, "C").Value, Year, Month)
End If
End If
End If
Next Month
Next Year
Next PartRow

' Message Box showing part numbers not uploaded from data

j = 2
Do While Worksheets(SourceWorksheet).Cells(j, "A") <> ""
PartNumbers(Worksheets(SourceWorksheet).Cells(j, "A")) = Worksheets(SourceWorksheet).Cells(j, "B")
j = j + 1
Loop

Msg = "Part #'s Not Loaded:" & vbCr

For j = 5000000 To 5200000
If PartNumbers(j) <> "" Then
For PartRow = Range("Forecast_MonthPartList").Rows(1).Row To Range("Forecast_MonthPartList").Rows(Range("Forecast_MonthPartList").Rows.Count).Row
If Worksheets("Forecast").Cells(PartRow, "C") = j Then
PartNumbers(j) = ""
End If
Next PartRow
End If
If PartNumbers(j) <> "" Then
Msg = Msg & j & " " & vbCr
End If
Next j

MsgBox Prompt:=Msg

Application.Calculation = xlCalculationAutomatic
Application.Cursor = xlDefault

End Sub

Have no idea where # is on your post screen. Tried to format things and a bunch of stuff came up instead of what I intended. never mind then I'll just delete this account.