Menu "Start" do not pop up in coherence

Hello,

I installed parallels a few weeks ago, and it works great!
last week there is something changed I think, but I can't find how to solve....

When I click on the icon of the windows XP start menu in the dock (in coherence mode) the windows Start menu do not pop up.

When I right click on the icon I can go to "Applications" ==> "Start menu".
After that the menu pops up

Thanks a lot for helping me!

Marco