What exactly is your problem?
For what I've seen and read, the ettercap is not stable in BT5, so people is uninstalling or removing it from the distro and re-installing the deb package built for this ubuntu distro on which BT5 is based..
This way works.
Please, be more specific as to what your problem is, so we can help you, because in this thread, the problem was "ettercap hanging when scanning for hosts" and it has been solved.
BEst of lucks..