You don't have to remove the following instruction
when you apply the following diff because patch command
will ignore this instruction.

How to apply the diff and re-make:

cd /path/to/DaqComponents/src
patch --backup < /path/to/this/2009.10.monitor-fatal-error.patch
make -f Makefile.Monitor

--- Monitor.cpp	Wed Mar 31 12:25:37 2010 +0900
+++ Monitor.cpp	Wed Apr 07 14:38:27 2010 +0900
@@ -531,6 +531,7 @@ int Monitor::daq_run()
 		fatal_error_report(USER_ERROR2, -1);
 		std::cerr << "cannot convert canon mod number to monitor private module number"
 				  << std::endl;
+		return 0;
 	}
     m_evs->Increment(0, &m_cdata[0], event_byte_size / EVENT_BYTE_SIZE,
 		m_monitor_priv_modno[modNo]);