Windows Defender Error 0x800705b4 appears during program installation and sometimes when you run any windows update.

Try this,

Error code 0x800705b4 fix – How to fix code 0x800705b4 error quickly?_Windows Error Help (http://www.windowserrorhelps.com/error-code-0x800705b4-fix-how-to-fix-code-0x800705b4-error-quickly)

Let me know if it helps.