Simple Dot Rendering

Question

First I want to say I'm very new to directx. I'm trying to build a simple game. I already have a loop and sort of GameTimer. With this I was able to render a "color-fading" background. But offcourse I want more ;-). I'm trying to render a group of dots. this is my dot-array: public CustomVertex.TransformedColored[] DotData; And I'm trying to fill it this way: for(int i = 0; i < 100; i++) { DotData[0].X = rand.Next(100); DotData[i].Y = rand.Next(100); DotData[i].Z = 1.0f; DotData[i].Rhw = 1.0f; DotData[i].Color = Color.FromArgb(rand.Next(200) + 55, rand.Next(200) + 55, rand.Next(200) + 55).ToArgb(); } Compiling goes well, but when i launch the application I get this error (translated from dutch to english): The appication generated an exeption wich cannot be processed. Process-id=0xb48 (2888), thread-id=0xf04 (3844) Click OK to close the application. Click CANCEL to track errors in the application. When I click cancel it says the error-tracker isn't available. And when I click OK the application exits. This code produces the same error: DotData[0].X = 10; And when I comment that line all works well (no dots offcourse, but I do see the fading BG). Does anyone know what is wrong? Thanks in advance, Jules