We certainly fought through our fair share of NDMP troubleshooting, and even placed a call with a very helpful EMC tech, who almost got us going completely.  It seems some large portion of our issue, is that our Symantec Backup Exec 12.5 install, will half-way talk over the NDMP protocol with the VNCe 3100 in it's vanilla config.  However, it won't actually work - until you enable the NDMP Option, in the setup of Backup Exec.  There's an additional license for it, but you can get a 60 Day trial, by turning it on in Add/Remove Programs.  You can see if it's enabled, under the License Information button on the About page of Backup Exec.  Once the NDMP Option is on, you'll see the VNCe show up by IP, in the NDMP Severs Node in Backup Exec selections list - and things will work much better from there on.   Otherwise, you can only see it show up in the User-Defined Selections (assuming you put it there) - where it will apparently, be doomed to fail.
Our organization recently purchased a VNXe 3100 to use as a NAS with CIFS shared folders.  We are attemping to use our Backup Exec to make backups of some of the data being shared on these drives since many documents are critical to the organization.  We purchased the NDMP option for Backup Exec, enabled NDMP and set a password on the share but when we attempt to add the NDMP Server on Backup Exec we receive an error saying:  "Unable to authenticate with the NDMP server, or with the remote comptuer that is configured as a Remote Media Agent, or with the remote computer that is configured for deduplication"  I have tried multiple passwords, tried both the VNX IP address and the shared folder address.  I am able to ping both and the VNX is able to ping our Backup Exec system.  I contacted EMC yesterday and they weren't able to figure out a solutution.  Does anyone have any ideas?  I am brand new to this process and after two days of Googling have found no real answers.
VNXe 3100 backing up with Backup Exec NDMP Option