Error when setting some sheets in code but not with others - vba

Question

I have a large macro for automating invoices for my company. Sometimes we have proforma invoices that mean we delete two of the three invoices that are manipulated (Client, Owner, and VAT). Therefore I have to check before each code is run whether the sheet exists.
The problem I've run into is that it will give me a run time error 424 when I set some of the sheets to be checked. In the code below it is the second time that the TVA sheet is checked for where the error occurs (If TVASheet Is Nothing Then). Mind you I have almost exactly the same code running above it except it is checking for ClientSheet instead.
'If the current payment is the only payment then we add to the TVA invoice
'that the rest is due
'on the date the balance of rental is due
If (Range("F3") <> "" And Range("G3") = "" And Range("H3") = "") Then
On Error Resume Next
Set TVASheet = Sheets("TVA Invoice")
On Error GoTo 0
If TVASheet Is Nothing Then
Else
Sheets("TVA Invoice").Select
If Cells.Find(What:="du paiement sera reçu", After:=ActiveCell, LookIn:= _
xlFormulas, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _
xlNext, MatchCase:=False, SearchFormat:=False) Is Nothing Then
Cells.Find(What:="Select!F3", After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
MatchCase:=False, SearchFormat:=False).Activate
ActiveCell.Offset(1, 0).Select
Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.Font.Bold = False
ActiveCell = _
"=100 - 100*TEXT(Select!F3,""0%"")&""% du paiement sera reçu le ""&PROPER(TEXT(Select!C30,""JJ-MMMM-AAAA""))&"""""
Else
End If
End If
Else
On Error Resume Next
Set TVASheet = Sheets("TVA Invoice")
On Error GoTo 0
If TVASheet Is Nothing Then
Else
Sheets("TVA Invoice").Select
If Cells.Find(What:="du paiement sera reçu", After:=ActiveCell, LookIn:= _
xlFormulas, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _
xlNext, MatchCase:=False, SearchFormat:=False) Is Nothing Then
Else
Cells.Find(What:="du paiement sera reçu", After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
MatchCase:=False, SearchFormat:=False).Activate
ActiveCell.Rows("1:1").EntireRow.Select
Selection.Delete Shift:=xlUp
End If
End If
End If
Sheets("Select").Select

Answer 1

Declare your TVASheet variable at the beginning of your code:
Dim TVASheet As Worksheet
Obviously the "TVA Invoice" sheet is not found and the Set command fails. Because of your On Error Resume Next the program continues and the interpreter has no clue what TVASheet should be in your If clause. You can avoid this by the declaration.