Why can't I disabled my lockscreen?

[AC Question]

I have a HTC One M8 and can't recall exactly when I was no longer to disable the lock screen - at the moment the only option not grayed out are:

Pattern
PIN
Password

I've read some articles about clearing credentials however that is grayed out also.

I'm on Android Version 5.0.1

Any help would be much appreciated

Thanks!

 

[B. Diddy]

Welcome to Android Central! Go to Settings>Security>Device Administrators. Is anything there checked besides Android Device Manager?