Eraser not working on mask

[handypandy1]

Thanks for the quick reply. I have used the erase to the mask for many years. I initially learned it from the video below, to cut to the chase go to about 4 minutes in. I don't want to waste your time, so it will save me a long winded explanation. I'm familiar with your method, but this erase method is just my long standing habit.
https://www.youtube.com/watch?v=9GBfn6aW6a8&t=555s