I am having the same problem.
I installed 2 different rocketheme templates and its the same error.
The frustrating part is there is no way to debug. The only error we can get from logs is
child died with signal 11
Nothing more than this.
Again the other templates works fine, so it is something to do with gantry and rockettheme template.
Is there any way at least we can debug or get what is the error ?