I've had this a couple of times now. I have added the iToo ForestPack folder's bitmap path to the external paths in 3ds max, but sometimes on a crash it seems like this path (and only this one) is removed from the paths list. This happens even after a normal scene save and reboot, so it's not because of "unsaved layout" in max pre crash.
I get the attached error when rendering.
I can't see the bitmap path as missing in asset tracking - so that's weird.
I add the path manually again (not the x86 folder, but other one where the maps actually are located). Run "relink bitmaps" plugin to be safe and then all works again.
Any ideas? It's all local + I have added network paths to our server where we have a copy of the iToo folders, but this doesn't seem to help (though those paths always remain after a crash).