DragonHawk

You're out of signaling channels.

In the stock config, the BCM 400 has a 2/6 DS30 bus split, which gives you 64 signaling channels. Various things consume signaling channels, including IP phones, media bays, voice mail ports, etc.

See the "BCM Networking Configuration Guide" (Nortel P/N N0060606), Chapter 5, "Configuring application resources", for the full explanation, including how to figure out how many of the various BCM resources you'll need.

BEM -> Config -> Resources -> Telephony Resources -> select bus 1 (IP Apps & Sets) -> IP Terminal Details tab, make sure all the IP sets that are listed really exist, and are in active use. Maybe you've got IP sets you don't really need/want.

If you have few or no TDM sets, you can change to a 3/5 bus split to gain signaling channels for IP sets. Make a backup first. Going from 2/6 to 3/5 is supposed to preserve BCM config, but it's still a big change. RTFM first. "Changing the DS30 split" of Chapter 5.

css_ets01

Sometimes we may have configured some IP sets and removed from port just like that without enabling keep alive.
Though they may not appear in Element manager they tend to be virtually blocking the numbers.
So you first enable the keep alive for all existing IP sets and then go try to disable and enable the IP Sets and trunks.

This will terminate all the existing IP sets registered and the only keep alive sets will be back to normal and the virtual sets will be removed completely.

Now you can register more.

But anyway the first suggestion of changing the split would be a best option if this doesn't work out.