I installed the latest MikTex2.9 and tested the following simple code trying to create a node in a tree diagram. 

```
\documentclass{article}
\usepackage{graphics,graphicx}
\usepackage{pstricks,pst-node,pst-tree}
\begin{document}
\pstree[radius=3pt]{\Tcircle{X}}
\end{document}

```

But I received the following error: 

```
"Undefined controlled sequence. \pstree[radius=3pt]{\Tcircle{X}}"

```

Any hints what went wrong? Thanks!