Viewport animation playback freezes

Hi,
I would like to ask if anyone has encountered this problem and knows how to resolve this.
It is kind of frequent for me to encounter realtime animation playback hanging problems in 3dsmax.
i am currently working with 3dsmax 2009 x64, but i have encountered this in previous versions.

Basically the problem is:
lately i have been working with rigging and character animation, so i'm not sure if it applies only to this situation, or also others.
after i animate my character, i click on the play button, on the animation controlling panel, and my viewport gets updated only for some 5 or 10 frames, then it hangs, like if it got stuck. the frame slider also gets stuck. i have enabled statistics, and statistics show that the viewport is being updated at nearly 50fps. the character is low polygon (game design), so it is not a performance issue, i guess.
i have also tried using point cache modifier, and disabling below modifiers, so the skin mesh doesn't need to be computed in real time, but the problem continues.

it's painfull that i have to export a preview animation and loop it in an external program everytime i want to see if the result is ok..
when animating characters, in a walking loop, for example, it's essencial to be able to preview the loop playback in realtime.

hope anyone can give me some help here =)
cheers