workbook sharing entries at the same time
 

Hi everyone,
Let`s say I have one workbook which is shared by 40 different users on
a network,this workbook has 3 objects such as,userform1,textbox1 and
commandbutton1.Once commandbutton1 pressed the following code is
activeted;
Private Sub CommandButton1_Click()
Cells(Rows.Count, "A").End(xlUp).Offset(1, 0).Select
Selection.Value = TextBox1.Value
End Sub
it`s very basic right?But if user A,user B and user C open this
workbook from different computer and press the commandbutton1 before
they save the workbook there will be a message for ;three different
users try to change the cell value,which entry excel needs to
consider(sorry I don`t literary remember this message by word)is there
a way to prevent that message and textbox1.value enter in the next
below cell?If the question is not clear please let me know.
Thanks for your help.