When I first start up windows, I get this error message every time:
Application failed to initialize: 0x80070006. The handle is invalid.
Anyone got any ideas what might be causing it, or ideas of things to try?
Do you, or did you, have another antivirus on there recently? How about running now? AVG, Norton, etc.? This looks like your problem:
And this is how to disable it and stop the message:
I believe it means the Windows Defender service is disabled, but you haven't also disabled it through the "Windows Defender" applet in the Control Panel. There's a small program that is set to run on start up that works together with the Windows Defender service (probably to provide the tray icon) which isn't disabled/enabled with the service.
Either go into the Control Panel and uncheck the box "Use this program", or get a utility such as Sysinternal's Autoruns and stop Defender from launching on startup. This is assuming you don't want to run it.
If you did want to run it, you probably just need to go to Administrative Tools -> Services and make sure Windows Defender is set to "Automatic" and is enabled.