No output returned from plugin but services shows ok

I'm trying to check the system memory by using check_memory.pl and the following command setup:

In the nrpe.cfg on the remote host

    command[check_mem]=/usr/lib/nagios/plugins/check_mem -f -w 20 -c 10

Service on the Nagios server:

define service{
use                     generic-service
host_name               Hostname     ;winserver
service_description     Check Memory
check_command           check_nrpe!check_mem
}

When I run the command on the remote host like this

/usr/lib/nagios/plugins/check_mem  -f -w 20 -c 10

I get:

OK - 73.6% (6013416 kB) free.|TOTAL=8175616KB;;;; USED=2162200KB;6540492;7358054;; FREE=6013416KB;;;; CACHES=2021812KB;;;;

When I run

/usr/local/nagios/libexec/check_nrpe -H host-ip -c check_mem
or
/usr/local/nagios/libexec/check_nrpe -H host-ip -c check_mem -a -w 20 -c 10

or any list of args

I receive :

   Wrong Syntax: custom_check_mem 
   Usage: custom_check_mem [-w|--warning]<percent free> [-c|--critical]<percent free>   

but the Web is showing Service is OK and a message like this:

(No output returned from plugin)
Wrong Syntax: custom_check_mem

Usage: custom_check_mem [-w–warning] [-c|–critical]

I tried this plugin on other servers it work well but I don't do what is missing in the setup for this one.

Any help is appreciated. Thanks