Delete Collection Object

I am getting below error while running the function. Please suggest what's wrong in my code.

Code:

[Button: AJModify]
    Title    : Delete Bill
    Action: Call: ModifyVouchers
    Key: Ctrl + T

[#Form: Daybook]
    Button    : AJModify, RefreshTDL
    Local : Button    : Refresh TDL    : Key    : Ctrl + S


[Collection: SelectedVoucher]
    Data Source : Report    : Selected
    Keep Source    : Yes



[Function: ModifyVouchers]
    Variable    : VCHID    : String
   
    100    : Walk Collection    : SelectedVoucher
        1000: Set    : VCHID    : "ID:" + $$String:$MasterId
        1010: Call    : ModifyVoucher    : ##VCHID
    110: End Walk


[Function: ModifyVoucher]
    Parameter    : VCHID    : String
    Variable    : VNumCount    : Number
   
    Object    : Voucher    : ##VCHID

    090    : Set Target
    100    : Walk Collection    : All Ledger Entries
    110    : Set Target
        1100    : Set    : vNumCount    :$$NumItems:BillAllocations
        1110    : While    : ##vNumCount > 0
            2110    : Delete Collection Object    : BillAllocations    :    1    :    Yes
            2120    : Decrement    : vNumCount
        1120    : End While
    120    : Set Target    : ..
    130    : End Walk
    140    : Set Target    : ..
    150    : Accept Alter
   
    

 

there should be atleast one bill allocation ...

 

Yes, There are. Still I'm getting error.