Using graphics to draw on form, in C#
new Pen(y)



This should be disposed.




Graphics g = Application.OpenForms["Client"].CreateGraphics();



I wonder why are you getting the Graphics object like this? To redraw something you should actually handle the Paint event or override the OnPaint method where you get a ready to use Graphics object from the system. And of course like @Cody Gray said, you need to dispose a graphics object acquired this way.



Those try/catch blocks are suspicious too. There is nothing that could throw an exception. If this runs every 100ms there is no room for exception handling. This would be very bad for the performance.