Suggest you add handling to test if any of the sheets to be renamed already exist:
Sub Test()
Dim ws As Worksheet
Dim ws1 As Worksheet
Dim strErr As String
On Error Resume Next
For Each ws In ActiveWorkbook.Sheets
Set ws1 = Sheets(ws.Name & "_v1")
If ws1 Is Nothing Then
ws.Name = ws.Name & "_v1"
Else
strErr = strErr & ws.Name & "_v1" & vbNewLine
End If
Set ws1 = Nothing
Next
On Error GoTo 0
If Len(strErr) > 0 Then MsgBox strErr, vbOKOnly, "these sheets already existed"
End Sub