midi volume automation track does not affect the volume

That is precisely my problem. When I modify/automate in Cubase the volume of a midi track linked to an Halion instrument using cc7 or by moving the volume fader of the midi track on the MixConsole, it has no effect whatsoever on the volume of the Halion sound. Same with pan. In Cubase, I can see the Volume values change according to my automation but that does not have any effect on Halion and its volume does not change.
I really don’t understand what I am doing wrong. Again, it works fine with Kontakt vst intruments.