Code:
Private Sub btnSave_Click()
Dim ctrlno As String
Dim filename As String
ctrlno = TextBox1.Text
MsgboxResult = MsgBox("Do you already have a referral folder created on your computer?", vbYesNo, "Retail Investment Sales Referral Form")
If MsgboxResult = vbYes Then
    existingfolder = InputBox("Please enter the name of the folder in which your referral files are contained:", "Retail Investment Sales Referral Form")
    existingfoldercheck = "c:\" & existingfolder
    If Dir(existingfoldercheck, vbDirectory) <> "" Then
        filename = existingfoldercheck & "\" & ctrlno & ".xls"
        
            ActiveWorkbook.SaveAs filename:= _
            filename, FileFormat:= _
            xlNormal, Password:="", WriteResPassword:="", ReadOnlyRecommended:=False _
            , CreateBackup:=False
    End If
Else
    If MsgboxResult = vbNo Then
    Dim InputBoxResult As String

    InputBoxResult = InputBox("Please enter a name for the folder to which you will be saving your referrals in:")
    NewDir = "C:\" & InputBoxResult
    'ChDir "C:\"
    MkDir (NewDir)
    NewDirMsg = "Your referrals will be saved in:" & NewDir
    MsgBox NewDirMsg
    filename = NewDir & "\" & ctrlno & ".xls"
        ActiveWorkbook.SaveAs filename:= _
            filename, FileFormat:= _
            xlNormal, Password:="", WriteResPassword:="", ReadOnlyRecommended:=False _
            , CreateBackup:=False
    End If
End If
End Sub
Say for instance the file tries to save over itself and it asks the user "as;lfk already exists, would you like to overwrite the file?" They click "Cancel". Well, when they click cancel it comes up with an error:

Run-time error '1004'
Method 'SaveAs' of object '_Workbook' failed.

How do you keep that from happening?