Page 15 :HTTP Error 400 Bad request

Introduction

The Web server (running the Web site) thinks that the data stream sent by the client  was 'malformed'

i.e. did not respect the HTTP protocol completely.

So the Web server was unable to understand the request and process it.

400 errors in the HTTP cycle

Any client  goes through the following cycle:

• Obtain an IP address from the IP name of the site  This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs).
• Open an IP socket connection to that IP address.
• Write an HTTP data stream through the socket.
• Receive an HTTP data stream back from the Web server response. This data stream contains status codes whose values are determined by the HTTP protocol. Parse this data stream for status codes and other useful information.

Fixing 400 errors - general

There is a low-level problem in the client or the Web server or both. 95% of the time this is because of a problem on the client system
e.g. there is something unstable on your PC running the Web browser.

• Try to browser again in three times to make sure that error
• What has changed since you started getting the HTTP 400 problem ?. In general terms, think about what has changed on your PC since you first started seeing the problem. This may cover any of the items mentioned above.

• How stable is your Internet connection ?.You can  try to check that the Web site you are actually visiting is the one you think you are visiting. For example, you may have a DNS problem. You can check this using a ‘ping’ test. A DNS problem may be caused by your ISP or may be on your own system e.g. in a ‘hosts’ file.

• Is your PC secure ?. If your PC is not well-protected, then all kinds of problems may occur - including HTTP 400 errors. If you run Windows, stay uptodate with automatic security updates from Microsoft and possibly consider getting a registry cleaner. Always have good anti-virus and spyware protection. Invest in a hardware firewall if you can afford one. Be sensible surfing the Web - block pop-up windows and avoid bad sites. If your PC not secure then Web traffic out from your PC to the Internet may be secretly corrupted by malware (spyware, viruses, etc.).
• Are you installed web-based software ?. Some social networking and games sites ask you to download and run software on your PC so you can interact with other people on the Internet directly (without using your Web browser). This software, if badly written or even criminal, can corrupt all HTTP traffic from your PC. At bad action, you may have to reinstall your operating system again (possibly losing all your personal data on your PC if you do not have backup).may be defective. Try to find an upgrade or security fix for the problem browser. 
• If you recently changed some configuration options in the problem browser, reversing the change to see if that helps to fix this problem.
• Do you get the error on big Web sites ?. If you get the problem on quite a small site, visit some of the bigger sites like Amazon, Ebay, Google, Microsoft and Yahoo. If you get the problem only on small sites, it indicates a problem with only those sites or the traffic from your PC to those sites.
• Do you get the error on simple URLs ?. If you get a problem with a long complicated URL (such as http://www.xxx.com?PHPrequest=643&value=dres&cookies=No) but not with a shorter simpler URL for the same site (such as http://www.xxx.com), this can indicate a problem with the Web server on the site you are trying to visit. This is not conclusive evidence, but is a good starting point. Contact the owners of the Web site and describe the problem to them. You may find for example the problem occurs with POST methods (you are both submitting data to the Web site and retrieving data from the Web site), but not with GET methods (you are only retrieving data from the Web site).
• Do you have a cache problem ?. clearing your cookies, browser cache and browsing history in your Web browser. Disable or remove any third-party cache or ‘web accelerator’ software you installed. Then try rebooting your PC . If this action  not fix the error, but at least may eliminate any problem due to settings on your PC.