NoMemoryError: failed to allocate memory

I’m using daemons to control a script that should always run on
background in my development server. But, when I start the script it,
returns this error:

<MissingSourceFile: no such file to load – fast_xs>
<NoMemoryError: failed to allocate memory>

The script itself runs anyway, but failing to start threads (I use a
threadpool with a low number of threads and I have a begin …
resume … block that makes the script run anyway).
Actually the thing is driving me crazy is that this error happens only
when I “start” the daemon (e.g. ruby script/my_daemon start);
everything is ok if instead of starting it I “run” it (e.g. ruby
script/my_daemon run).

Any suggestion?