I've found these things in my poser 4 and 5 runtimes. I'm on a amc computer. what do you think?
ImageIO_Mac_M.mrw

Try renaming it, and see what happens. I'm curious about whether this tip works for Macs, too. If the Mac version really needs the file, you can always name it back.

I, too, find that dumping this file really speeds things up. I think it is related to the size of the runtime, and I guess mine are kind of bloated. It's noticeably faster, navigating around the library.