NFS via internal network at BuyVM

I have multiple servers at the LV location (OpenVZ), including a storage vps (KVM).

I have configured a NFS server on the storage server. But when I try to mount the server on the other OpenVZ servers, I either get a "device not found" error message or "nfs invalid argument".

I get the "device not found" error message when I dont specify NFS4 and "nfs invalid argument" when specifying NFS4.

The internal ip of the OpenVZ servers are in the allowed host and "showmount -e 172.16.." does display the available mount paths.

Anybody have working NFS on the internal network ?