The "p1_file" directive is not saved by monarch engine when you import a nagios.cfg file.
So when you commit to recreate a configuration, Nagios doesn't want to restart :
nagios.log:
[1218199440] Error: p1.pl file required for embedded Perl interpreter is missing!
[1218199440] Bailing out due to errors encountered while initializing the embedded Perl interpreter. (PID=21293)