Problems Monitorinf File Age in a Windows Server


I have some problem configuring de FileAge option. Using NC_net agent.
I have searched for documentation with no luck related with the formar the command should have in the service definition.
Lets say I have a file in the path C:\flag.txt which I have to monitorize. It shouldn’t be there more than 10 minutes.
The command is define correctly in commands.cfg.

check_command check_nsc_fileage!C:\flag.txt!600!900

What I get in the Nagios Web Interface, Status Information. is “No counter specified”

Am I missing one step??

Thanks in advance