error 577 when i attempt to turn on windows defender win8.1

http://answers.microsoft.com/en-us/protect/forum/protect_defender-protect_start/windows-defender-not-working-after-upgrade-to/51ff2e69-b7e7-46da-84c9-392bf040ef1e

In the above thread we have seen that OP had same problem as yours and he tried some editing of registry that we normally do not recommend but it worked for him. You may want to give it a try. All you have to do is to:

1. Press Win key + R. This will open Run.
2. Type "regedit" and hit enter.
3. Navigate to these keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Defender 4. Change value of 'DisableAntiSpyware' and 'DisableAntiVirus' from '0' to '1'. 5. After changing the values go to 'C:\Program Files\Windows Defender' and open 'MSASCui.exe' file.

Hope this will fix the problem.

This error seems to be of Windows rather than of Windows Defender. Please post a question in Windows 8.1 forum, they can help better.

I have seen some more cases like this and I think the problem is specific with Windows Defender only. I want you to try this:

Turn off Windows Defender by going to Settings --> Administrator and unchecking "Turn on this app" and clicking "Save Changes". After turning off Windows Defender, open Registry Editor (in Start menu search for regedit.exe and open it). After opening Registry Editor, navigate to this registry key:

KEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services and change values of 'Start' and 'Type' entries according to the following:

WdBoot -->

Start: 0

Type: 1

WdFilter -->

Start: 0

Type: 2

WdNisDrv -->

Start: 2

Type: 1

WdNisSvc -->

Start: 2

Type: 16

WinDefend -->

Start: 2

Type: 16

Example:

Note: Incorrect editing of registry can cause serious damage to system. And you are doing edits in very sensitive area of registry. So be very careful. If you didn't understand anything then stop and ask it. I will explain in simpler words.