[CentOS] NFS mount problem

Hi,guys:

I am trying to connect to a NFS-filesystem on a CentOS 5.3 i386 guest system. The host system is CentOS 5.4 x86_64. I set up the NFS server correctly and rpcinfo is also ok inside the guest system show.

The problem is, I can't connect to, or see the open port from the outside. I use the Host-Only network setup with VirtualBox 3.1.0, the ip address in the guest system is 192.168.56.101 . and the host system ip address is 192.168.7.67

When I mount the directory from the guest system via NFS, the result is the following : "mount : 192.168.56.101:/xx failed , reason given by server:Permission denied"

I hope one of you can give me a hint in which direction I should continue my efforts.

Thanks in advance,,,