AIX 5.3 check_nrpe --> check_mem unable to read output c


I try to monitor an Aix 5.3 server with nagios and nrpe. I can check many services (disk space…) but I got a problem with the memory. When I execute the command on the AIX server check_mem -w 70 -c 90 I’ve got this error check_mem[10]:check_mem/ not found and on the nagios server:
/usr/local/nagios/libexec/check_nrpe -n -H **** -c check_mem -a 70 90
I’ve got:
NRPE: Unable to read output.

Thank you to your help