I used to have problems with things like that, double posting, not being able to use the Java client at work, and what not. In addition to Windows being a steaming heap of elephant dung I'd say Brad is right, one of a number of network protocols or, browser settings are probably to blame.
My best advice is to poke around with Internet Options for a bit, but I suspect that unless you've got an up-to-date browser, it's going to have a bit of problems with PHP on occasions.
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Please replace the handset, and try again.