Monit can't stop tasks if timeout option is used and its value is greater than 2147 seconds, complaining "failed to stop (exit status -1) -- Program ... timed out". To reproduce the issue just create "stop program" statement on 32-bit system with timout option > than 2147 seconds, i.e. 2148. I suppose that "start program" will also fail (not tested, though). The issue might be related to 32-bit long *timeout in control.c.
Issue #267 resolved