HTTP Error 400 Bad Request

The HTTP 400 error occurs if the HTTP header is too long. In principle, headers don’t have a size limit, however, the target server may have set a limit. The header consists of several fields, in which requests and answers are defined. If both callers have matched the parameters, the requested data will be exchanged. If this doesn’t work, an error message will be displayed. Because this involves communication between the browser and the webserver, and 400 errors are usually caused by problems with the client, the browser is probably responsible for the error. The best way to test whether your default browser could be the cause of the problem: temporarily switch to another browser.

If the page can be accessed using your test browser, switch back to your original web browser. Delete all your cookies (if you haven’t already done so). For security reasons, it is best to delete them all instead of just one. Cookies are transferred in the header and this is how the webserver learns about your previous visit. If the browser ends up having to process too many requests, it could mean that the header will exceed the length limit.

If this solution doesn’t work, you could try reinstalling the browser completely or resetting it to its default settings. Depending on which browser you use, there are different ways to reset it. For Firefox, type in about:support for troubleshooting. Here, you will find plenty of information that will help you detect errors in the software. Even if you contact a support team, it’s still important to have this data. On this page, you will see a button that enables you to 'clean up Firefox'. When you click on it, it will delete extensions and some settings, but will keep your current settings.

In Internet Explorer, you can find the 'Reset' button in the internet options under the 'Advanced' tab or 'Restore defaults' (under IE 6). The Microsoft browser lets you choose whether you want to delete your personal settings when resetting. Since Internet Explorer also counts cache and cookies as these types of settings, it is recommended to delete these too.

With Chrome, you will find the reset functions in the system settings. The browser keeps your personal data, like stored passwords and history, but returns everything else to its original state. Close the browser and restart it for the changes to take effect.