I've had the same problem with ZShare since Tuesday:
- Videos on ZShare.net don't work under Firefox, just get this message:

- The same links stream fine under Internet Explorer.
- The same links stream fine under Firefox when embedded (e.g. when hotlinked on a linkhunting site).
I was thinking it was an incompatibility with the site's code and Firefox, but another PC on my router accesses the page and streams the same videos just fine... so I'm confused. :S
Anyone got any ideas on what could be causing it? I've checked a whole laundry list of things and have also tried to recreate the problem on a different system, with no luck.
I've also noticed that a lot of the other (inferior!

) linkhunting sites have stopped posting ZShare links - I imagine because of the same problem, though that's pure speculation.
Hopefully a solution'll appear soon... unfortunately there seems to be no info out there on this problem at the moment.

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EDIT: Here's a list of the things I've tried, in case it helps anyone:
- Cold-booted the machine a coupla times to "clean out the cobwebs" - no change.
- Tried using Firefox Portable v2.0.0.20 with no add-ons - makes no difference.
- Malware scanning with Spybot/Malwarebytes/ESET - removed a couple of minor infections, system is now clean with no more infections reported.
- Logging-on to ZShare - makes no difference, videos still 404-ing.
- Checked the HOSTS file against the HTTPFox entries for the ZShare page - with no luck.
- Using Firefox on a different PC on the same router connection - plays the video fine from a ZShare.net link.
As a different PC linked through the same router can see the videos on ZShare.net, the problem would seem to be on my machine... so it's not an ISP or country block. Also changed my MAC a few times in case ZShare was possibly blocking it - no change.
I simply can't see why the video files - which are definitely available to be streamed - are giving 404 errors on one machine and not another. I'm beginning to think this may be the result of settings being corrupted from a bit of malware; definitely leaning towards a repair install, hoping it may fix the problem.***********************