Not working: Main group-> stock groupwise-> item total

Writing a code: Main group wise-->Groupwise--> item report for sales, but even though the sample "stock groupwise item total" tdl works fine, adding a main group parameter does not gives the expected result. The inventory item part fails to explode.
What am i missing ??

The format I am expecting is as follows if a Sales voucher has 8 items which are assigned to their groups which are also assigned to a higher level group:

INVOICE​

------------------------------------------------------
Main Group-1

Sub Group-1

Item 1---Qty---Rate---Disc--Amount
Item 2---Qty---Rate---Disc--Amount​

Sub Group2

Item 3---Qty---Rate---Disc--Amount
Item 4---Qty---Rate---Disc--Amount​

--------------------------------------------------
Main Group-2

Sub Group-3

Item 5---Qty---Rate---Disc--Amount
Item 6---Qty---Rate---Disc--Amount​

Sub Group-4

Item 7---Qty---Rate---Disc--Amount
Item 8---Qty---Rate---Disc--Amount​

--------------------------------------------------

P.S: If I remove the "TSPL FFEMainGroup" part, it shows the collection OK, but of course without MainGroup.


Here is the code i have tried so far.
;----------------------------------------
[#Form: SalesColor]
Add : Print : TSPL FFEInvoice

[Report: TSPL FFEInvoice]
Use : Printed Invoice
Delete : Form
Add : Form : TSPL FFEInvoice

[Form: TSPL FFEInvoice]
Use : STDInvoiceDimensions
Part : TSPL FFEMainGroup
Space Top : 0 mms
Space Bottom : 0 mms
FetchObject : Stock Item: @@InvEntryList: Parent

[Part: TSPL FFEMainGroup]
Lines : TSPL FFEMainGroup
Repeat : TSPL FFEMainGroup : TSPL MainGroup Coll
Scroll : Vertical

[Line: TSPL FFEMainGroup]
Fields : TSPL FFEItemMarks1, TSPL FFEItemPackages1, TSPL FFEItemDescription1, TSPL FFEItemQty1, TSPL FFEItemRate1
Right Field : TSPL FFEItemAmount1
PrePrinted : Yes

Local : Field : TSPL FFEItemMarks1 : Set As : $MainGroupName
Local : Field : TSPL FFEItemPackages1 : Set As : ""
Local : Field : TSPL FFEItemDescription1: Set As : ""
Local : Field : TSPL FFEItemQty1 : Set As : ""
Local : Field : TSPL FFEItemRate1 : Set As : ""
Local : Field : TSPL FFEItemAmount1 : Set As : ""

Explode : TSPL FFEItemsDes

[Part: TSPL FFEItemsDes]
Line : TSPL FFEStockGroup
Repeat : TSPL FFEStockGroup :TSPL FFE Inv StkGrp Coll
Scroll : Vertical

[Line: TSPL FFEStockGroup]
Fields : TSPL FFEItemMarks, TSPL FFEItemPackages, TSPL FFEItemDescription, TSPL FFEItemQty, TSPL FFEItemRate
Right Field : TSPL FFEItemAmount
PrePrinted : Yes
Empty If : #TSPLFFEItemMarks1 ! = $MainGroupName

Local : Field : TSPL FFEItemMarks : Set As : ""
Local : Field : TSPL FFEItemPackages : Set As : $Name
Local : Field : TSPL FFEItemDescription : Set As : ""
Local : Field : TSPL FFEItemQty : Set As : ""
Local : Field : TSPL FFEItemRate : Set As : ""
Local : Field : TSPL FFEItemAmount : Set As : ""
Local : Field : TSPL FFEItemPackages : SubTitle : Yes
Local : Field : TSPL FFEItemPackages : Variable: StockGroupName

Explode : TSPL FFEStockItemsPart

[Part: TSPL FFEStockItemsPart]
Lines : TSPL FFEItemsDetails
Repeat : TSPL FFEItemsDetails : TSPL FFE Inv Coll
Space Bottom: 2 mms
Vertical:Yes
Scroll : Vertical

[Line: TSPL FFEItemsDetails]
Fields : ItemMarks,ItemPackages,ItemDescription,ItemQty,ItemRemarks
Right Field : ItemAmount
Empty If : #TSPLFFEItemPackages ! = $Name

Local : Field : ItemMarks : Set As : ""
Local : Field : ItemPackages : Set As : ""
Local : Field : ItemDescription : Set As : $StockItemName
Local : Field : ItemQty : Set As : $BilledQty
Local : Field : ItemRemarks : Set As : $Rate
Local : Field : ItemAmount : Set As : $Amount


[Collection: TSPL FFE Inv Coll]
Source Collection : ..
Walk : Inventory Entries
Fetch : *.*
Compute : Name : $Parent:StockItem:$StockItemName

[Collection: TSPL FFE Inv StkGrp Coll]
Source Collection : TSPL FFE Inv Coll
Fetch : *.*
By : Name : $Name
Compute : MainGroupName : $Parent:StockGroup:$Name
Aggr Compute : TotGroupAmount : SUM : $Amount

[Collection: TSPL MainGroup Coll]
Source Collection : TSPL FFE Inv StkGrp Coll
Fetch : *.*
By : MainGroupName : $MainGroupName
Aggr Compute : TotMainGroupAmount : SUM : $TotGroupAmount

[INCLUDE: vchfld.tdl] ; just contains field info to simplify the main code.