Merge excel cells issue using VB.NET - vb.net

Question

Hello everyone and thank you!
I have some wierd exception that I cannot solve.
It is not my first program though I cannot figure it out!
I'm writing an application wich through it I want to fill an excel workbook.
every time i'm trying to merge cells, I'm recieving an error.
I have checked over and over and I just can't figure it out.
everything in my code supposed to work.
the xl application,workbook,worksheet and ranges all declared.
the wierdest is that if during the code running, i'm entering the excel worksheet manualy (after pausing the program with a msgbox or something), and
selecting some cell (no matter wich), the code is running just fine :(((
Im not aloud to add in images so here is the code - copy paste.
the btn click code:
Private Sub btnCreatPriceQuote_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnCreatPriceQuote.Click
oXL.Visible = False
Dim indexForCopy As Integer
'few commands for faster run in the xl WB
XlFasterRun()
'Replace pricequote sheet with its format to avoid overwrite
PriceQuoteRenew()
'Decalre rows for add details on the BAMAY
DecalreFirstRow()
FillPriceQuoteTable()
TillIndex = 39
EmptyCellIndex = 13
the declaration from a module:
`Public Sub DecalreFirstRow()
rng1thcol1thLinePQ = shPriceQuote.Range("A75:D75")
rng2thcol1thLinePQ = shPriceQuote.Range("E75:F75")
rng3thcol1thLinePQ = shPriceQuote.Range("G75:H75")
rng4thcol1thLinePQ = shPriceQuote.Range("I75:J75")
rng5thcol1thLinePQ = shPriceQuote.Range("K75:L75")
rng6thcol1thLinePQ = shPriceQuote.Range("M75:N75")
rng7thcol1thLinePQ = shPriceQuote.Range("O75:T75")
rng8thcol1thLinePQ = shPriceQuote.Range("U75:X75")
rng1thcol1thLineCF = shCusFile.Range("A12:G12")
rng2thcol1thLineCF = shCusFile.Range("H12:K12")
rng3thcol1thLineCF = shCusFile.Range("L12:O12")
rng4thcol1thLineCF = shCusFile.Range("P12:S12")
rng5thcol1thLineCF = shCusFile.Range("T12:W12")
rng6thcol1thLineCF = shCusFile.Range("X12:AA12")
rng7thcol1thLineCF = shCusFile.Range("AD12:AI12")
rng8thcol1thLineCF = shCusFile.Range("AJ12:AN12")
End Sub
`
public sub where the exception occured:
Public Sub FillPriceQuoteTable()
With rng1thcol1thLinePQ
.Select()
.Value = rng1thcol1thLineCF.Value
**.Merge()**
End With
With rng2thcol1thLinePQ
.Select()
**.Merge()**
.Value = rng2thcol1thLineCF.Value
End With
With rng3thcol1thLinePQ
.Select()
**.Merge()**
.Value = rng3thcol1thLineCF.Value
End With
With rng4thcol1thLinePQ
.Select()
**.Merge()**
.Value = rng4thcol1thLineCF.Value
End With

Answer 1

Replace:
rng.Merge()
With:
rng.mergecells=true.