Integer not storing correct LastRow value after many loops: VBA Run-Time error - vba

Question

In the code below, my LastRow variable is not storing the right row number on the 27th loop (i = 27) causing the code to malfunction
I have used the F8 step through multiple times and noticed that the issue is on the 27th loop. The LastRow variable is meant to be +1204 rows from the previous LastRow value on each iteration of the loop, so I was expecting LastRow = 32509 instead of LastRow = 31316. For reference, on the 26th loop, LastRow = 31305. I'm not sure why the it is finding the wrong LastRow when the code has worked for the first 26 loops.
I am trying to get from my Source Table to my Desired Table:
Source Table
to
Desired Table
Also , the final error that shows is:
Run-Time error '1004': Application -defined or object- defined error
Sub Populate_entity()
Dim i As Integer
i = 1
Dim LastRow As Long
Dim SearchText As String
Do While i < 122 ' go across entity (columns wise)
If i = 1 Then
Range("E1").Select
Selection.Copy
SearchText = ActiveCell.Value
ActiveCell.End(xlToLeft).Select 'snap to left (cell A1)
ActiveCell.Offset(0, 2).Select 'move to cell C1
ActiveCell.Offset(1, 0).Select ' move to cell C2
Else
ActiveCell.Offset(0, i + 1).Select
Selection.Copy
SearchText = ActiveCell.Value
ActiveCell.End(xlToLeft).Select
ActiveCell.Offset(0, 2).Select
ActiveCell.End(xlDown).Select
ActiveCell.Offset(1, 0).Select
End If
ActiveSheet.Paste
ActiveCell.Offset(1203, 0).Select
ActiveSheet.Paste
ActiveCell.End(xlUp).Select
' ======== Error here ========
LastRow = Cells.Find(What:=SearchText, After:=ActiveCell, LookIn:=xlValues, SearchOrder:=xlByRows).Row
Range("C" & ActiveCell.Row & ":C" & LastRow).FillDown
ActiveCell.End(xlUp).Select
i = i + 1
Loop
End Sub

Answer 1

A summary of what you want, as you described in the comments:
Copy the values from cells E1:DU1, paste each cell 1204 times in column C.
1st loop it will paste cell E1 in C2:C1205
2nd loop it will paste cell F1 to C1206:C2409
etc.
This code achieves that:
Sub Populate_entity()
' Declare 2 range variables (top row to copy from and paste destination)
Dim RowRange As Range
Dim PasteCells As Range
' Use the With block to specify the sheet. If you want the destination
' to be another sheet, then you can specify that instead:
' ThisWorkbook.Sheets("SheetName").Range("...")
With ThisWorkbook.ActiveSheet
Set RowRange = .Range("E1:DU1") ' Set range to copy from
Set PasteCells = .Range("C2:C1205") ' Set paste cells, blocks of 1204 cells in column C
End With
' Loop through RowRange, copy each cell's value into PasteCells
' Then offset the PasteCells range by 1024 rows, so next RowRange cell
' is inserted underneath previously copied cells.
Dim ofst As Long
For ofst = 1 To RowRange.Cells.Count
' Use .Value to avoid the (comparably slow) copy/paste operation
PasteCells.Offset((ofst - 1) * 1204, 0).Value = RowRange.Cells(ofst).Value
Next ofst
End Sub

Answer 2

In my opinion you don't need any search because your code always places the SearchString in row 1205. Since you know that it is there you don't need to look for it. This thought brings me to the code below.
Sub Populate_Entity()
Dim C As Long ' Column
Dim Target As Range
Dim FirstRow As Long
Dim LastRow As Long
FirstRow = 2
LastRow = 7 '1205
C = 3
Range("C2").value = Range("E1").value
' Cells(2, C).Value = Cells(1, 5).Value
Do
Set Target = Range(Cells(FirstRow, C), Cells(LastRow, C))
Target.FillDown
C = C + 1
Cells(2, C).value = "Can't figure"
Loop While C < 3 ' 122
End Sub
I have cut the loop short to only 7 rows (instead of 1205) and 3 columns (instead of 122). I just couldn't figure out where the text in the FirstRow should come from. For column C it comes from E1, but where does it come from in the subsequent columns? You can fill this in using the method I showed you above, like, Cells(2, C).Value = Cells(1, 5).Value. I believe that the 5 can be replaced by a value derived from the current C, perhaps C + 2.
Note the Cells(2, C).Value doesn't refer to the value in cell C2. Instead if refers to the cell in Row 2, Column C.