The HTTP 400 Error

The HTTP 400 error translates to Bad Request. It can sometimes be seen when attempting a logon to a website unsuccessfully.

In short, the server cannot process your request - potentially due to malformed URLs, corrupted cookies or outdated DNS data.

You can try flushing the DNS cache as well:

ipconfig /flushdns

which should yield the output "Successfully flushed the DNS Resolver Cache" if successful.