When I open a folder in thumbnail mode that contains folders containing images (so 4 small images appear in each thumbnail of the folder) Opus crashes quoting an error number (0xC0000005) in a thread at an address. There are also several Haali Media Splitter icon in the system tray that disappear when the mouse moves over them.
I can avoid this by not displaying thumbnail mode but if there is an image in the folder, Opus will switch automatically to thumbnail (I know I can stop it from auto switching but I'd rather not).
I'm using Server2008 but it was happening on Vista 32bit previously and I am using the latest Opus 9.
Almost certainly an issue with particular movie file(s) in that folder triggering a crash in either one of your installed video codecs or in the Haali Media Splitter.
There are alternative codecs & splitters which seem problem free in the FAQ on movie playback:
If you want to try different ones I would uninstall Haali and any codec packs first.
FWIW, I would try uninstalling Haali first, then install whichever splitters you need from the list in the FAQ and see if that solves the problem. I say that because over the years I've seen so many threads about Haali crashing that I'd suspect it before anything else. (Although I have never used it personally so maybe I'm jumping to conclusions about the quality of its code.)