Exchange 2007 backup failt with status 71

I just had a look at NBU 7.6 DB SCL. It seems that 7.6.1 client should work.

Is this standalone or clustered Exchange? 

How was Exchange backed up until now (bearing in mind that NBU8 is brand new)?

Can you navigate Exchange Management Console using the same user logon?

Although this is not GRT backup, you may want to go through this TN to ensure all is fine as far as service logon is concerned.
http://www.veritas.com/docs/000068163

NetBackup 7.6.0.3 for Exchange Administrator's Guide  contains quite a number of requirements as far as credentials are concerned.
Have you configured Exchange properties in Client's Host Properties?  

I also see this on p.37: 
If you configure the NetBackup Client Service with a logon account and configure
the Exchange credentials in the Exchange client host properties, you must
configure the “Replace a process level token” for both users

More on page 45:
Configuring the account for NetBackup Exchange operations (Exchange 2007)

Page 88:
Policy recommendations for Exchange Server 2007 backups 

I expect your configuration to work. NetBackup 7.6.1 can back up Exchange 2007. The Windows version is not important. (I can't prove this; my Windows 2003 server was carted away last year.)

I'm concerned with what you mean by the following:

> ... when I open the BAR from the client...

By "BAR" do you mean the Windows BAR application, nbWin, sometimes referred to as the MFC GUI, or were you using the remote NetBackup Console? Assuming the former, under which account did you open the BAR application?  Did you use "Run As..."?

The purpose of executing the NetBackup Client Service as a certain account is so that it will execute various client processes (bpfis, bpbkar32, tar32, etc.) with the account.

> ... when I ran a manual backup...

Do you mean that you configured a policy and invoked "Run manual backup" in the NetBackup Console with that policy? Or did you ask the BAR application to back up something?  Or did you execute bpbackup from a command window?  If you ran a policy manually (as opposed to on a schedule), how did you create the backup selection list for the policy?

Error 71 is "files don't exist," which is equivalent to your woes in the BAR app.

For Exchange 2007, NetBackup supports both snapshot backups and "streaming" backups, by which we mean using an Exchange API that "streams" the backup data to bpbkar32.  Which kind of backup did you try?

I think for Exchange 2007 you don't need to configure Exchange credentials in the client host properties, and I think you don't need to worrry about the privilege to replace a process token. Configuring these would do no harm. I can confirm whether you need them if necessary.