VB API: Using model action listener

Hi everybody. I'm working in C# with Creo4. I want to ask how I correct use a listener in Creo. My problem is that when I ask from my application to open some model in Creo, next I need feedback - model was opened. I decided to use model action listener. It's working, but after 5times, Creo frozen and stop working, I think that there is something what I do wrong. My simple code is attached, could somebody help me? It driving me mad...

Thanks a lot.

Radoslav