[CentOS] error mounting NFS client on NFS server

My NFS server is on 192.168.10.10, with the following setup in /etc/exports: /backup 192.168.10.0/24(rw)

Then, form a client (192.168.10.11), I run mount 192.168.10.10:/backup /bck, but get the following error: root@vps01 [~]# mount 192.168.10.10:/backup /bck mount.nfs: Input/output error

On the main server, I see this in /var/log/messages: Mar 8 08:42:52 venus kernel: kjournald starting. Commit interval 5 seconds Mar 8 08:42:52 venus kernel: EXT3 FS on dm-6, internal journal Mar 8 08:42:52 venus kernel: EXT3-fs: mounted filesystem with ordered data mode. Mar 8 08:43:02 venus mountd[10383]: authenticated mount request from 192.168.10.11:989 for /backup (/backup)