Monitoring Websphere in ND with security

Hi,

I try to evaluate Application Manager for monitoring our Websphere Application Servers.
We have IBM WAS 6.1.0.7 in cluster (ND) with security activated (LDAP with windows).
I installed the IBM perfServletApp.ear in server1 (JVM) and activate the PMI in some servers.
I try the test URL and have this error:
<PerformanceMonitor responseStatus="failed" version="6.1.0.7">
−<Comments>
Could not determine process type.

com.ibm.websphere.management.exception.AdminException: javax.management.JMRuntimeException: ADMN0022E: L'acc�s est refus� pour l'op�ration getParent sur le MBean Discovery en raison de justificatifs insuffisants ou vides.
at..........

Is someone can help me?
Another question: Do we have a monitor for each JVM/Application or just one monitor for the WAS environnement? We have about 30 JVM by environnement (Prod, Dev, Test. PreProd).