I suspect you might be running a non-stock gtk+ version. Please attach the complete output of running "plank -d" in a terminal.
This could also be a duplicate of https://bugs.launchpad.net/ubuntu/+source/gtk+3.0/+bug/1478175
I suspect you might be running a non-stock gtk+ version. Please attach the complete output of running "plank -d" in a terminal.
This could also be a duplicate of https:/ /bugs.launchpad .net/ubuntu/ +source/ gtk+3.0/ +bug/1478175