ProjectItemEvents not fired with a custom project

Hello,

I have developed a DSL, with custom solution, project and file type.

I have also a custom ToolWindow in which there is a DropDown list that contains the list of the items in the loaded solution. 

I succeed to update the content of the dropdown when a solution is opened or closed.

I want alos that it is updated when the user add/remove/rename a file into a project. Here is the code:

this.projectItemEvents = dte2.Events.SolutionItemsEvents;
this.projectItemEvents.ItemAdded += SolutionItemsEvents_ItemEvents;
this.projectItemEvents.ItemRemoved += SolutionItemsEvents_ItemEvents;
this.projectItemEvents.ItemRenamed += SolutionItemsEvents_ItemRenamed;

The problem is that the events are never fired.

Can anyone tell me what I'm doing wrong?

Thanks in advance.