I posted back about this a while back and my example/explanation of the problem wasn't quite correct and failed to take notice. What I have found, and should be addressed, is that, in my own tests, approximately 300-400 vst plugins for windows out of about 800 I have do not work correctly with the vst~ object in max/msp.
What is happening is one of two things. In the first, less volitile situation, the Max scheduler is completely frozen. In the second scenario merely loading the program causes max to freeze, and, the task manager is required to close it down, if you can manage to open it.
So I made a small patch and included a few plugins, one which works, and one which doesn't. Please, try it out and tell me what you think.
Here is the patch: http://bine.aporre.com/vst_scheduler_interface.zip
So, you load the first plugin, all is fine. Load the 2nd one, and the scheduler craps out. In regards to the 2nd plugin, like I said, I have tested about 800 plugins and about half of them suffer from this. A few of my plugin programming friends said that the problem was VSTGUI. I notice this kind of behavior in Cubase and such, but, the main difference between these 2 applications is that, in Cubase, it'll still keep the timing and midi events won't be frozen while the mouse button is down! Graphical updates will cease, but the timeline still goes forward and you can hear the musical information you've put in. Doing the same in max/msp completely freezes everything, so if you had some chords going into this Vst~ object from say, an external midi source, they wouldn't be heard until AFTER you released the mouse button, meaning, well, it's bad :/
Thanks for your time,