flickering skybox (newb question)

Hi, I'm using C# from Visual Studio 2003 and DX9 for this. Basically, I just
created a skybox into a panel control on a windowed form, and I'm rotating
it. The rotation is done by a timer that goes off every 50ms, and increases
the "dblAngle". The problem is that there is a lot of flicker. (I hope I'm
posting enough info. If not, please tell me what else to post!)

Here is how I'm setting my presentParams:

presentParams.SwapEffect = SwapEffect.Discard;
presentParams.BackBufferFormat = Format.X8R8G8B8;
presentParams.BackBufferHeight = this.Height;
presentParams.BackBufferWidth = this.Width;
presentParams.BackBufferCount = 3;
presentParams.PresentationInterval = PresentInterval.Default;
presentParams.EnableAutoDepthStencil = true;
presentParams.AutoDepthStencilFormat = DepthFormat.D16;
device = new Device(0, DeviceType.Hardware,
this.panelMain, CreateFlags.HardwareVertexProcessing, presentParams);

Here is how I'm setting up my matrices:

device.Transform.World = Matrix.Identity;
// dblAngle is incremented by a timer going off every 50ms
device.MultiplyTransform(TransformType.World, Matrix.RotationY(dblAngle));

device.Transform.View = Matrix.LookAtLH( new Vector3( 0.0f, 0.0f, 0.0f ),
new Vector3( 0.0f, 0.0f, 400.0f ), new Vector3( 0.0f, 1.0f, 0.0f ) );

device.Transform.Projection = Matrix.PerspectiveFovLH((float)Math.PI/4.0f,
(float)this.Width/(float)this.Height, 1.0f, 500.0f );

Here is my render:
private void Render()
if (device == null) return;

//Clear the backbuffer to a Green color
device.Clear(ClearFlags.Target | ClearFlags.ZBuffer,
System.Drawing.Color.Green, 1.0f, 0);

//Begin the scene
// Setup the world, view, and projection matrices

device.VertexFormat = CustomVertex.PositionColored.Format;

device.SetTexture(0, null);
device.SetStreamSource(0, vbTerrain, 0);
device.DrawPrimitives(PrimitiveType.TriangleList, 0, 2);

// draw the skybox

//End the scene

catch (DeviceLostException)
// etc.

Aaron Lovi,
Poker Villain support
support [at] pokervillain.com