Concurrent Access Handling in C# Form Application

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C#

server

DataGridView

I have developed A system for Customer management system. this is an client server application. multiple users can access the system from the server on same time. So I have an Interface which is contains Datagridview with multiple rows.
My prob is:
Once a user clicked on a row from a location, at the same time another user from another location cannot click on the same row. if he clicked the same row there should popup a message box with showing that "Already another user accessing the same row....."

So Please me to sort this Problem
Thanks in advance... :)