The webpage cannot be found - HTTP 400

Instead of the login window, you only see this warning:

The text is:

The webpage cannot be found - HTTP 400

Most likely causes:

• There might be a typing error in the address.
• If you clicked on a link, it may be out of date.
• What you can try:
• Retype the address.
• Go back to the previous page.
• Go to and look for the information you want.

Cause

The browser cache in Internet Explorer is preventing Citavi from loading the login page correctly.

Solution

1. In Windows click Search.
2. Enter Internet Options.
3. Click the General tab.
4. In the Browsing history section, click Delete.
5. Enable the checkboxes for at least one of the following:

• Temporary Internet files and website files
• Cookies and website data
• History

6. Click Delete.
7. Click OK. 
8. Restart Citavi 6.

If this doesn't help, please follow these steps:

Windows 10 and 8

1. Click Search.
2. Enter Internet Options.
3. To enable cookies, on the Privacy tab, click Advanced and then enable the First-party Cookies checkbox.
4. Add an exception for Citavi: Click the Privacy tab > Sites > Enter citavi.com in the Address of website field and click Allow.
5. To enable Javascript (Internet zone): On the Security tab, click the Internet zone > Custom level > Scripting > Active scripting and then click Enable.
6. To enable Javascript (Trusted sites): On the Security tab, click Trusted sites >  Custom level > Scripting > Active scripting and then click Enable.
7. Add trusted sites by clicking Security > Trusted sites > Sites. In the Add this website to the zone field, enter https://citaviweb.citavi.com and https://code.jquery.com/
8. On the Advanced tab, select the Use TLS 1.2 checkbox:

9. Click OK.
10. Restart Citavi 6.

Windows 7

If you're still using Internet Explorer 8, please update to Internet Explorer 11, even if Internet Explorer isn't your default browser.

1. Click the Windows button to open the Start menu.
2. Click Control Panel.
3. Click Network and Security.
4. Click Internet Options.
5. To enable cookies, on the Privacy tab, click Advanced and then enable the First-party Cookies checkbox.
6. Add an exception for Citavi: Click the Privacy tab > Sites > Enter citavi.com in the Address of website field and click Allow.
7. To enable Javascript (Internet zone): On the Security tab, click the Internet zone > Custom level > Scripting > Active scripting and then click Enable.
8. To enable Javascript (Trusted sites): On the Security tab, click Trusted sites >  Custom level > Scripting > Active scripting and then click Enable.
9. Add trusted sites by clicking Security > Trusted sites > Sites. In the Add this website to the zone field, enter https://citaviweb.citavi.com and https://code.jquery.com/
10. On the Advanced tab, select the Use TLS 1.2 checkbox:
    
11. Click OK.
12. Restart Citavi 6.
13. A faster option is to reset your settings of the Internet Options: Select the Advanced tab. In the Reset Internet Explorer Settings dialog box, select Reset.