tpautoconf -report_disc

***EDIT***
Can they be seen ok at the OS level?
Has Removable Storage Manager service been stopped & disabled on the servers in question?

Check with the issue servers whether in device manager drive is showing properly and windows driver is installed properly . And also verify whether SSO license is in place on tht servers.

If you can able to see the drive in device manager then delete the missed path entry from GUI and then reconfigure the tape drive only for the problematic servers.

 Rajesh 

You did not mention the drive type and the driver used?
I know a lot of users recommend using Vendor driver, but I have only ever seen this problem where the vendor driver was used - never with the Symantec drivers.
On x64 O/S we can only use vendor drivers. This is what we've done to elimate these problems with IBM tape drives:
1. Disable RSM
2. (extract from device compatibility guide):
If using the IBM Windows Tape Device Drivers be sure to choose the install_nonexclusive.exe executable. This option permits a tape drive to be accessed by multiple processes on a Media Server, which is a requirement for NetBackup.
NetBackup requires the IBM Data Path Failover feature to be disabled on the IBM tape device driver. To disable this feature, open the reg folder of the IBM driver package, double-click DisableDPF.reg, and reboot the system.
- IBMTape driver level 6.1.9.5 tested on Windows
3. Disable TUR as per TechNote: http://seer.support.veritas.com/docs/268245.htm

Please note if this hasn't been done already, but the tapes drives need to be persistently bound to the HBA, preferrably in the same order across all the Windows media servers. This will keep your OS drive mapping the same after rebooting the Windows server.
Can you tell if this mapping issue happened after the server was rebooted?

media server rebooted but still same issue missing path

I have never seen a reboot fixing missing path issue (talking from experience).
Maybe have a look at the rest of the suggestions?

when
in
doubt
weboot
system

that said, we do have some windows servers, and I would follow Rajesh' advice

robot details : IBM     03584L32        7379
drive details : IBM     ULT3580-TD3     73P5        

getting this output in GUI

yesterday i delete the drives from media server then configured them but still same missing path error

Can I repeat my 1st post?

This is what we've done to elimate these problems with IBM tape drives:
1. Disable RSM
2. If using the IBM Windows Tape Device Drivers be sure to choose the install_nonexclusive.exe executable. This option permits a tape drive to be accessed by multiple processes on a Media Server, which is a requirement for NetBackup.
NetBackup requires the IBM Data Path Failover feature to be disabled on the IBM tape device driver. To disable this feature, open the reg folder of the IBM driver package, double-click DisableDPF.reg, and reboot the system.
- IBMTape driver level 6.1.9.5 tested on Windows
3. Disable TUR as per TechNote: http://seer.support.veritas.com/docs/268245.htm

run scan , use Disk Management to very the drive path,  go to symantec website download Tape Device Drivers to reconfigure tape drive, after run Configure Tape Drive Wizard. Good luck :)

Once the path is missing on a Windows media server (becasue persistant binds were not setup) the drive mapopings in the registry are whacked. Rebooting will not fix the issue. The drives WWn will need to be manually assigned for persistent bindings to maintain the pathing during a reboot. It will most likely take a couple of reboots to get this cleaned up.

Once the OS can see the tape drives (while persistenatly bound to the HBA) load the drivers using the non-exclusive option.
Configure the tape drives on the media server using the java console and then you should be all set.
The key is starting this process out correctly from the begining.

Once you have a missing path on the tape drive, you need to delete the drive from the NBU master (EMM).

Try the following steps

1. set devmgr_show_nonpresent_devices=1

2. Go to Device management and  in the options select show hidden devices.

3. Delete all drives and then run tpautoconf -a

4. Install the drivers for the drive and reboot the server once.

This should fix your issue.