Fix a Bad Request Error 400

1. Utilizing the Windows Restore configuration.
2. Downloading and installing the service pack for .NET Framework onto your computer.
3. Editing the Windows registry with the Microsoft Registry Editor program.

1. Click Start button, then click All Programs.
2. Click Accessories and then click System Tools.
3. Choose the “System Restore” option. The “System Restore” dialog will appear.
4. Select the “Restore my computer to an earlier time” option and click the “Next” button.
5. Select a checkpoint before the error appeared and click the “Guided Help (Registry Backup)” option. 
6. Click the “Next” button. Click the “OK” button and click “Next.” The computer will undergo the restoration process and restart.
7. After the Windows system boots up, click the “OK” button in the “System Restore confirmation” window.

Answer two:

1. Download the Microsoft .NET Framework 1.1 Service Pack 1 from below:
2. http://download.microsoft.com/download/8/b/4/8b4addd8-e957-4dea-bdb8-c4e00af5b94b/NDP1.1sp1-KB867460-X86.exe
3. Click the “Save” button in the prompt and select a destination location for the file. Find the file and double-click the file to run it.
4. Clcik desktop Start button, and then click Run. Type ”Regedit” into the “Run” in the text field and click the “OK” button. Then you will see registry editor appear.
5. Go to the left-side pane and navigate to the following entry: “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ASP.NET.” 
6. Find “VerificationCompatibility” in the right-side pane, right-click it and select “Modify.” Alter the “Value Data” to “1” and click “OK.”

Answer three:

I have ever used a registry cleaner software. Many of my friends and collegues also use it. It is a very good tool to resolve Bad Request Error 400 and many other computer problems. You can follow below steps:

1. Download and install registry cleaner to your computer.
2. Start registry cleaner and on the interface click Scan button.
3. When the scan process is finished, click Repair All button.