Call to i:im() in application debugger failed in ejabberd

I'm trying to debug ejabberd. I have compiled the files with debug_info. I start ejabberd, then use ejabberd debug to get into the shell. Once in there, running im() produces "Call to i:im() in application debugger failed". I can't figure out what's causing this. Any ideas o开发者_如何学Gon how to debug?

Edit

I've tried running this in just the erl shell independent of ejabberd and it still fails. So it looks like it's related to my erlang setup as opposed to a problem with my ejabberd setup.

Foolish me: apt-get install erlang-debugger solved the problem.