We encounter this with some regularity. Also using RH 8.0.2 but on both XP and Windows 7 machines. We import Word docs with embedded images and often the images don't transfer. Like you, when generating WebHelp locally,everything looks great but once we publish, the images are gone, not even an "X" to show where there should be images. We've noticed that sometimes RH does not even create the xxx_files folders.
We're eager to see what resolutions there may be. Thanks.
I will note that I've seen forum posts about missing files, but nearly all of them seem to be related to Word.
We're not using Word at all; we're generating content directly in Robohelp.
Two possibilities here.
Try a different image format just for the purposes of ruling out the current pngs. If that works, try saving the PNGs in a different app to whatever you used to create them.
Second, I'm pretty sure the RoboHelp application is not supported on Windows Server. You may have been using it successfully to date but you can play Russian Roulette and get away with it, for a while!
See www.grainge.org for RoboHelp and Authoring tips