Error 91 displays after Application Quit instruction - excel

Question

I have built an Add-In which is intended to be downloaded from the www. The Add-In will land up in the user computer's Downloads folder.
On being activated, the first phase of the Add-In's activty is to copy itself into the user's '/Microsoft/AddIns' folder using SaveAs. Then then "parent" Add-in closes itself and quits Excel. (On restarting Excel the "child" Add-In will be loaded and active.)
The code for this is
Sub CheckInstall()
'Several lines of code before this.
'They have been tested and seem to work well.
MyNewfileNm = TestBase & GCSAPPNAME
If IsInstalled(MyNewfileNm) Then
Application.DisplayAlerts = False
ThisWorkBook.SaveCopyAs MyNewfileNm
Application.DisplayAlerts = True
MsgBox "We're done, and Excel will close." & Chr(13) & _
"On reopening you will find 'ACBA Mapping' loaded and active in the ADD-INS tab."
Excel.Application.Quit
ActiveWorkbook.Close False
Else
ThisWorkBook.SaveCopyAs MyNewfileNm
If ActiveWorkbook Is Nothing Then
Workbooks.Add
Set oAddIn = Application.AddIns.Add(MyNewfileNm, False)
oAddIn.Installed = True
Else
Set oAddIn = Application.AddIns.Add(MyNewfileNm, False)
oAddIn.Installed = True
End If
MsgBox "We're done, and Excel will close." & Chr(13) & _
"On reopening you will find 'ACBA Mapping' loaded and active in the ADD-INS tab."
Excel.Application.Quit
ActiveWorkbook.Close False
End If
End Sub
This processes and copies itself as expected, but before the Application.Quit completes I get an Error Code 91. On clicking the error message, it simply resumes the instruction code.The result is precisely as expected.
However, I must either solve the problem generating the error message or suppress the error message. For the time being I cannot do either.
I'd be grateful for a solution.

Answer 1

This turned out to be a silly mistake on my part. The revised code below runs without an error. The only difference is the elimination of the instruction to close the ActiveWorkbook in the first portion if the primary IF statement. There was no open workbook available to be closed at that juncture.
Sub Check Install()
'Several lines of code before this.
'They have been tested and seem to work well.
MyNewfileNm = TestBase & GCSAPPNAME
If IsInstalled(MyNewfileNm) Then
Application.DisplayAlerts = False
ThisWorkBook.SaveCopyAs MyNewfileNm
Application.DisplayAlerts = True
MsgBox "We're done, and Excel will close." & Chr(13) & _
"On reopening you will find the " & NewMappingVersion & " version of 'ACBA Mapping' loaded."
Excel.Application.Quit
' In principle we haven't initiated a Workbook so there is no need to close it.
' ActiveWorkbook.Close False
Else
ThisWorkBook.SaveCopyAs MyNewfileNm
If ActiveWorkbook Is Nothing Then
Workbooks.Add
Set oAddIn = Application.AddIns.Add(MyNewfileNm, False)
oAddIn.Installed = True
Else
' This shouldn't be necessary, but leave it for the time being.
Set oAddIn = Application.AddIns.Add(MyNewfileNm, False)
oAddIn.Installed = True
End If
MsgBox "We're done, and Excel will close." & Chr(13) & _
"On reopening you will find 'ACBA Mapping' version " & NewMappingVersion & " loaded and active in the ADD-INS tab."
Excel.Application.Quit
ActiveWorkbook.Close False
End If
End Sub