Try this
Code:
Private Sub btnSaveCommand_Click()
Me.AppointmentDate.SetFocus
If Me.AppointmentDate = "" or isnull(Me.AppointmentDate) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.cboClient) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.cboSalon) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.cboSalon) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.cboStaff) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.cboService) Then
MsgBox "Please complete all fields"
ElseIf isnull(Me.ProductID) Then
MsgBox "Please complete all fields"
End If
Else
DoCmd.GoToRecord , , acNewRec
MsgBox "Thanks - Appointment Booked!"
End Sub