from within the LAN you must use your internal ip address (usually starting by 10 or 192)
from outside your LAN people must use your external ip address (anything that's not starting by 10, 192 or 127).
I think you are not following these rules at the moment you get the error.
the no-ip is just an alias for the external ip address, so it's useful only from the outside, and you must be sure it is updated.