My MonoBehaviour Doesnt seem to have PlayerPrefsX..?

I'm working on how to save my player position through PlayerPrefs but somehow it gives an Invalid DWORD32BIT value and ive read some topics about "PlayerPrefsX.SetVector3" something and ive been trying to somehow use it onto my script but it only returns me an undefined variable which is "PlayerPrefsX". Here is the topic of some topics that ive read and this one also.