Why am i able to join 2 anchor points once in a while and other times it will not work. What am i doing wrong?

Before digitizing (editing) you can choose this option in Tool panel.

Does anyone know why i am having trouble joining two anchor points? On certain areas it will work fine and on others it will not. What am i missing. It must be something very simple. Please help.

Thanks,

Did you ever get help with this issue?  If not, I can share with you what I've learned.   Leah