I haven't used check_procs on my local nagios box, so I just tried it and got same error as you.
So I went to my source directory:
then tested plugin plugins/check_procs and got same error.
I then downloaded nagios-plugins-1.4.0alpha1 from nagiosexchange and did the same thing.
ran the check_procs check and it's ok. So you do the same please.