jit objects crash Max

Hi, I'm having a problem using jit. objects (have just started using Max) - any time I create one Max crashes (disappears, no error message)

I think it may be related to another problem outside of Max - certain videos consistently crash Finder on Quicklook and won't open in Quicktime either (so far seems to be only .mov & .mp4 filetypes, but not all of them - and they will open in VLC - perhaps something in my system has been corrupted? Have tried installing Perian to no avail)

Any ideas?

Max version 5.0.8
Mac OS X 10.5.8 2Ghz Intel Core 2 Duo

thanks
Jenny