Comment 8 for bug 1634412

Note that --on-fatal-error-abort is not a valid option, and just causes a warning to be emitted.

And if you specify a valid option twice, it should tell you explicitly:

$ /usr/sbin/unity-system-compositor --vt 8 --vt 8
[2016-10-27 13:29:27.409922] mirplatform: Found graphics driver: mir:mesa-x11 (version 0.24.0)
[2016-10-27 13:29:27.411185] mirplatform: Found graphics driver: mir:mesa-kms (version 0.24.0)
Failed to parse command line options: option '--vt' cannot be specified more than once.
usage: /usr/sbin/unity-system-compositor [options]
...

Sounds like either an old out of date unity-system-compositor is installed or something else completely is throwing that exception. I can't seem to make unity-system-compositor fail in a cryptic way like yours.