Web Forms :: Display File Is Locked Error Message When File Is Used By Another User

after i can copy my file to another folder i realised that if this webapplication is used by multiple users at once, then some users are going to get locked out because each one is trying to copy those files.

so how do i tell the user thats trying to use a file to wait untill the file is available.

StreamWriter WriterTotxt = new StreamWriter("date.txt", false);
DateTime LastAccess = File.GetLastWriteTime("path.dbf");
WriterTotxt.Write(LastAccess);
WriterTotxt.Flush();
WriterTotxt.Close();
string ReadTextFile = File.ReadAllText(txtFile);
DateTime test = Convert.ToDateTime(ReadTextFile);
if (File.GetLastWriteTime(LatestUpdatedTime).CompareTo(test) > 0)
{
File.Copy(Path.Combine(sourcefile, fName), Path.Combine(destinationfile, fName), true);
}