Was it work before or it is new implementation ?

Kindly run below command on master & post o/p.

<install_path>\prog files\veritas\netbackup\bin\admincmd>bppllist <policy_name> -L

What type of application you are trying to backup? Exchange, SQL or SharePoint?

omar i gues OP mentioned it.. it's MS TMG (forefront threat management gateway)

@ lary we need more granular detail for troubleshooting. could you please tell us how policy is created and how is infra between NBU and ESXi

It works for all the other virtual machines that we backup off the farm.

I think we got it narrowed down to the TMG server blocking the incoming connections from netbackup. It appears that netbackup can't get into the server to get the Application state of the MSSQL express database and so it fails, but it can get into ESXi to get the VMDK so the snapshot and the backup succeed. 

We are now just working on getting the proper ports opened between the TMG and netbackup

Charb were you able to conf TMG to allow the necessary NBU ports? Curious to see steps how you did it. I too am having an issue with NBU communication being blocked by TMG.