Hi Agni,
At the beginnig, I've programmed a much complex function wich opens a form to browse a sharepoint library, and the I've seen the crash, I replaced all my code with this one.
[InfoPathEventHandler(MatchPath=''CTRL1_5'', EventType=InfoPathEventType.OnClick)]
public void CTRL1_5_OnClick(DocActionEvent e)
{
// Write your code here.
...