VBA - Help with Union All

Hi

I have to track selective blocks of cells in a matrix that is 22 rows deep and
180 columns wide. WHICH blocks I need to track are determined by a drop-down.

Below is a snippet of code I tried using to accomplish this ......

    '-----------------
    '   DataStore
    '-----------------
    With WS_SByM
        Set RngDataStore = .Range("B2").CurrentRegion
        Set RngDataStore = RngDataStore.Offset(1, 0).Resize(RngDataStore.Rows.Count - 1)
        Set RngDataStore = RngDataStore.Offset(0, 1).Resize(RngDataStore.Rows.Count, RngDataStore.Columns.Count - 1)
        'Not Used
        DataStoreColCNT = RngDataStore.Columns.Count
    End With
    
    '-----------------
    '   Each Contractor
    '-----------------
    For c = 1 To ConCNT
        StartCol = 1
        '-----------------
        '   10 Blocks of Months
        '-----------------
        For iBlock = 1 To 10
            Set RngTmp = Nothing
            '-----------------
            '-----------------
            Select Case iBlock
                Case 1
                    Set RngTmp = Range(RngDataStore.Cells(c, StartCol), RngDataStore.Cells(c, NumberOfMonths))
                    Set oRngUnion = RngTmp
                    StartCol = StartCol + 18
                    EndCol = StartCol + (NumberOfMonths - 1)
                Case Else
                    Set RngTmp = Range(RngDataStore.Cells(c, StartCol), RngDataStore.Cells(c, EndCol))
                    Set oRngUnion = Union(oRngUnion, RngTmp)
                    StartCol = StartCol + 18
                    EndCol = StartCol + (NumberOfMonths - 1)
            End Select
        Next
        
        '-----------------
        '   THIS FAILS by 2nd pass thru the For loop - no errors
        '-----------------
        If Not oRngUnionAll Is Nothing Then
            Set oRngUnionAll = Union(oRngUnionAll, oRngUnion)
        Else
            Set oRngUnionAll = oRngUnion
        End If
        MsgBox "Area Count   " & oRngUnionAll.Areas.Count & "Address: " & oRngUnionAll.Address

Pass 1:
=========
?oRngUnion.Address
$C$2:$F$2,$U$2:$X$2,$AM$2:$AP$2,$BE$2:$BH$2,$BW$2:$BZ$2,$CO$2:$CR$2,$DG$2:$DJ$2,$DY$2:$EB$2,$EQ$2:$ET$2,$FI$2:$FL$2

?oRngUnionAll.Address
$C$2:$F$2,$U$2:$X$2,$AM$2:$AP$2,$BE$2:$BH$2,$BW$2:$BZ$2,$CO$2:$CR$2,$DG$2:$DJ$2,$DY$2:$EB$2,$EQ$2:$ET$2,$FI$2:$FL$2


Pass 2:
=========
?oRngUnion.Address
$C$3:$F$3,$U$3:$X$3,$AM$3:$AP$3,$BE$3:$BH$3,$BW$3:$BZ$3,$CO$3:$CR$3,$DG$3:$DJ$3,$DY$3:$EB$3,$EQ$3:$ET$3,$FI$3:$FL$3

?oRngUnionAll.Address
$C$2:$F$3,$U$2:$X$3,$AM$2:$AP$3,$BE$2:$BH$3,$BW$2:$BZ$3,$CO$2:$CR$3,$DG$2:$DJ$3,$DY$2:$EB$3,$EQ$2:$ET$3,$FI$2:$FL$3

In the 2nd pass the ORIGINAL ranges.addresses on oRngUnionAll are there
but the NEW range address related to oRngUnion have not been included.

I assume that Excel CAN DO this but that my approach is incorrect.

Any help is appreciated.

regards
John