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A couple of days ago, I started getting HTTP 400 responses from all websites. Nothing will go across port 80. However, everything works if I connect to VPN. The weird thing is, without VPN, other things still work; such as IM and anything else that doesn’t use port 80. Pinging also works.

I haven’t noticed this behavior on any other computer on my network. The kicker is, if I log on as a local admin, everything works fine!!!

I haven’t installed anything in the last couple weeks and I don’t remember changing any configuration. I ran Forefront and HouseCall and neither found any problems.

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For future visitors to this post: 400 is the status code for Bad Request (malformed syntax). – Pops Apr 5 '10 at 13:51
have you cleared your local iexplore cache? – tonyr roth Apr 5 '10 at 15:31
up vote 0 down vote accepted

I assume Windows can have different proxy settings for different connections. (That's true for a Mac.) So: maybe some proxy server is misbehaving?

For easy testing, Firefox allows for 4 different proxy settings:

  1. None
  2. Auto-detect
  3. Use system-wide settings
  4. Manual proxy configuration

I'd say: try the first option, and if that works then switch to the system-wide settings to see if things change?

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You pointed me in the right direction! Thank you. I wouldn't have even thought to check the proxy settings, since I haven't changed them in forever. However, I did have weird proxy settings setup. I pointed the proxy to This was in response to a bug in Office 2010 RC that I'm running. Somehow, that started acting up. I took that off and I'm back up and running. – Jason Sherman Apr 5 '10 at 16:03
@Jason, wow, so it was actually a non-working, non-existing proxy that made the browser connect to the actual website without any proxy after all? And that somehow changed the request? Odd! Any chance you could tell if the 400 errors were indeed generated by the remote websites? – Arjan Apr 5 '10 at 16:14

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