You can't turn on real-time protection in Microsoft Security Essentials (MSE).
This issue may occur if other security software, such as antivirus, antispyware, or antimalware programs, are fully or partially installed on the computer.
Make sure that all traces of the security programs that are installed on the computer are removed. This includes any free or trial products that were pre-installed when you bought the computer, even if those products were never activated. Also, make sure to completely uninstall the security program that you were using before you installed Microsoft Security Essentials. Some security programs have their own firewall. By removing these products, the Windows Firewall will be enabled. By default, MSE uses the Windows Firewall.
Note Security software typically includes antivirus, antispyware, or antimalware programs.
If you aren't sure which security programs are installed on the computer, you can use the AppRemover utility from OPSWAT, Inc. to identity the software. To obtain AppRemover, visit the following OPSWAT website:
After you identify the security programs that are installed on the computer or that have been partially removed from the computer, you can use a cleanup tool or instructions from the security program manufacturer to completely remove the program.
For more information about the cleanup tools that are available for a specific product, click the following article number to view the article in the Microsoft Knowledge Base:
2688686 List of security program cleanup and uninstall tools
After all other security programs are removed and the cleanup is completed, restart the computer, and then verify that Windows Firewall is turned on. You can check the status of Windows Firewall in the Action Center (or Security Center, if you are using Windows XP) or by using Control Panel.
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