The network server (running the website) considers that the data flow sent by the client (eg your browser) was 'malformed', that is, it did not fully respect the HTTP protocol. Therefore, the network server could not understand the request and process it.
This almost always means bad programming of the client system and / or network server.
Fixing Errors 400 - General
There is a low level fault on the client, the network server, or both. 95% of the time this happens because of a flaw in the client system, ie there is something unstable on the PC running the browser.
Is your PC secure? If your PC is not well protected then several types of problems can occur - including HTTP 400 errors. If you have Windows, stay current with Microsoft's automatic security updates and consider eventually getting a registry cleaner. Always have good anti-virus and spyware protection. Invest in a hardware firewall if you can get one. Be wise when surfing the Internet - block pop-up windows and avoid dangerous sites. If your PC's security is compromised, then the network traffic from your PC to the Internet may be secretly corrupted by harmful software (spyware, viruses, etc.) running on your PC. It may be difficult to detect this situation.
Installed software from the internet? Some social networking sites and games require you to download and run software on your PC, so you can interact with others directly on the Internet (without using the browser). This software, if it has been poorly designed or even criminal, can corrupt all HTTP traffic from your PC. It can be difficult to get rid of this defective software. At worst, you may have to reinstall your operating system again (eventually losing all the data you have on your PC if you have not backed it up).
Is your internet connection stable? If you have recently moved from ISPs or if your ISP is too slow or insecure then your PC traffic to any Internet site could be corrupt. Your ISP might have reconfigured some settings (for example, introduced new proxy or cache servers) that are causing some instability. If you can not easily navigate your ISP's website, this is a possible sign of trouble. You can also try to verify that the website you are visiting is the one you think you are visiting. For example, you may have a DNS problem. You can check this by using a ping test. A DNS problem can be caused by your ISP or it may be on your own system, for example in a hosts file.
Do you get the error on more than one website? If you get the error on many websites, this indicates that the problem is with your PC, not those sites.
Do you get the error if you use more than one browser? If you have two or more browsers installed on your PC and the behavior is not the same (one browser gives the HTTP 400 error when visiting one site and another does not give the 400 error when visiting the same site) then one of the browsers may be faulty . Try to find an update or a security fix for your browser problem. If you have recently changed some configuration options in the browser problem, try to revert the change to see if that resolves the situation.
Do you get the error on large websites? If you get the problem on a small site, visit some of the great sites like Amazon, Ebay, Google, Microsoft and Yahoo. If you get the problem only on small sites, this indicates a problem with only those sites or with the traffic from your PC to those sites.
Do you get the error in simple URLs? If you get a problem with long, complicated URLs (like http://www.xxx.com?PHPrequest=643&value=dres&cookies=No), but not with a shorter, simpler URL from the same site (such as http: // www .xxx.com), this may indicate a problem with the network server of the site you are trying to visit. This is not conclusive evidence, but it is a good starting point. Contact the owners of the website and describe the problem to them. You may find that, for example, the problem occurs with POST methods (either submitting data to the website or retrieving data from it), but not with GET methods (you are only retrieving data from the website).
Do you have a cache problem? Try clearing your cookies, your browser cache, and checking your browser history. Disable or remove any third-party cache or internet accelerator software that you have installed. Then try restarting your PC and any firewall / router you use to connect to the Internet. This may not resolve the error, but at least you can eliminate any problem due to old settings on your PC.
What has changed since you started having the HTTP 400 problem? In general terms, think about what has changed on your PC since the problem began to appear. This may include any of the items mentioned above. Pull back and check that the