I have recently been working at switching from daily tape backup to daily NAS backups of our 3 servers. I have been having difficulties getting the NAS to connect correctly. On the NAS software, I create a folder with no protection on it (Have done it with login accounts but I get same error). Once adding the NAS to BE, it will show as online for about 20 seconds, then go offline. Prior to adding, the folder was accessable via explorer, but after the drive goes offline the folder is no longer accessable via explorer: "Windows cannot access \\share\backupexec." When viewing just the share, the folder is shown. The only way I am able to "reset" things is by removing the drive in BE, deleting the folder on the NAS appliance via software, and then run "net use \\share\backupexec /delete" in command prompt.
Server 2008 R2, BE 2012 (Upgrade from 2010 R3 today)