check_mem nrpe unable to read output problem


i’v downloaded the check_mem plugin to remotly monitor memrory via nrpe.
nrpe has been all set up and is working. all the default commands are working.
i have the correct output.
but when i use the check_mem command, i have : NRPE : Unable to read output.
the check_mem command used in standalone mode work ok
i’ve already checked the permissions on the files and everything is ok.

./check_nrpe -H localhost -c check_mem ==> NRPE: Unable to read output
./check_mem -w 10 -c 5 ==> CRITICAL - 82 MB (4%) Free Memory

nrpe.cfg :
command[check_mem]=/usr/local/nagios/libexec/check_mem -w 10 -c 5

any ideas ? i’m stuck…