TAO Framework with VB.NET, gltranslatef does not work along z-axis

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OpenGL

HI,

The following code with TAO framework for OpenGL with VB.NET works well and draws a triangle:

Gl.glLoadIdentity()
Gl.glTranslatef(0, 0, 0)
Gl.glBegin(Gl.GL_TRIANGLES)
Gl.glVertex3f(0.2, 0.2, 1)
Gl.glVertex3f(0.7, 0.7, 1)
Gl.glVertex3f(0.8, 0, 1)
Gl.glEnd()

But when changing the z component of the gltranslatef function even by 0.1, nothing is drawn!
The following code draws nothing:

Gl.glLoadIdentity()
Gl.glTranslatef(0, 0, 0.1)
Gl.glBegin(Gl.GL_TRIANGLES)
Gl.glVertex3f(0.2, 0.2, 1)
Gl.glVertex3f(0.7, 0.7, 1)
Gl.glVertex3f(0.8, 0, 1)
Gl.glEnd()

I want to change the z component of the gltranslatef in order to move forward or backward.

gltranslatef works good with x and y axes; the problem is only with the z-axis.

Thanks to any help.