Well, this might be your problem:
you're using the command "check_nrpe", which asks the nrpe to be used with an argument, although you don't have one and you don't need one.
So, you might try to use your "check_nrpe_1arg" command instead (if you haven't already).
Also, check in your nrpe.cfg file that your check_load command is expected without any argument.
and, to finish: are you sure there's nothing in your syslog file about nrpe ? it should log every error nrpe encounters (I don't know the location of this file under debian, but try /var/adm/messages)
ps: sorry for my english; it's too early to write something clear but I hope you understand anyway ^^