Panic today – a guy couldn’t connect to Team Foundation Server with a weird “The request failed with HTTP status 417: Expectation failed.”
What did it happen? I never saw such a HTTP status code!
A bit of investigation explained the reason for it – the proxy he is using doesn’t support the expect100Continue behaviour, dropping the connection.
The guy used a proxy server indeed and he did not check the “Bypass proxy server for local addresses” checkbox. After checking that, he was able to connect to Team Foundation Server like everybody else.
It is also worth mentioning that this can impact also components like the Extension Manager, and you can bypass that setting by adding a node in the devenv.exe.config file - <servicePointManager expect100Continue="false"/>