vereato says:
WHERE @User_Name= '" & TxtBox_User_Auth.Text &"'
Here is the issue. You are setting parameter @User_Name in left side instead of column name.
Private Sub Update()
Dim ConnStr As String = ConfigurationManager.ConnectionStrings("MySQLConnect").ConnectionString
Using Conn As New MySqlConnection(ConnStr)
'Using Cmd As New MySqlCommand
Using Cmd As New MySqlCommand("UPDATE tbl_users SET Register_Time=@Register_Time, Last_Login_Date=@Last_Login_Date, PC_Name=@PC_Name, OS_Version=@OS_Version, IP_Address=@IP_Address WHERE User_Name=@User_Name")
Using Da As New MySqlDataAdapter()
Cmd.Parameters.AddWithValue("@Register_Time", DateTime.Now.ToString("T"))
Cmd.Parameters.AddWithValue("@Last_Login_Date", DateTime.Now.ToString("U"))
Cmd.Parameters.AddWithValue("@PC_Name", System.Environment.MachineName.ToString)
Cmd.Parameters.AddWithValue("@OS_Version", System.Environment.OSVersion.ToString)
Cmd.Parameters.AddWithValue("@IP_Address", Lbl_IP_Address.Text)
Cmd.Parameters.AddWithValue("@User_Name", TxtBox_User_Auth.Text)
Cmd.Connection = Conn
' Connect to Database
Conn.Open()
Cmd.ExecuteNonQuery()
'Conn.Dispose()
Conn.Close()
Cmd.Dispose()
End Using
End Using
End Using
End Sub