Sub AddSheetWithNameCheckIfExists()
Dim ws As Worksheet
Dim newSheetName As String
newSheetName = Sheets(1).Range("A1")
For Each ws In Worksheets
If ws.Name = newSheetName Or newSheetName = "" Or IsNumeric(newSheetName) Then
MsgBox "Sheet already exists or name is invalid", vbInformation
Exit Sub
End If
Next
Sheets.Add Type:="Worksheet"
With ActiveSheet
.Move After:=Worksheets(Worksheets.Count)
.Name = newSheetName
End With
End Sub