After restarting the backup server or the Backup Exec services, a job that is schedule to run may appear as "Ready; No media servers are available". If left for up to 20 minutes the job will start.

This can be caused by the Backup Exec Advanced Device And Media Management (ADAMM) service taking up to 20 minutes to timeout looking for non-existent devices. This can be seen in the log:

"C:\Program Files\Symantec\Backup Exec\Logs\adamm.log"

[4364] dd/mm/yyyy 11:34:33.203 Device: \\.\MediumChanger0
[4364] dd/mm/yyyy 11:34:33.828 Changer InitializeDevice() failed - ERROR = 0x00000006 (ERROR_INVALID_HANDLE)
[4364] dd/mm/yyyy 11:34:40.085 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)
[4364] dd/mm/yyyy 11:34:46.342 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)
[4364] dd/mm/yyyy 11:34:52.599 Device: \\.\MediumChanger0
[4364] dd/mm/yyyy 11:34:53.225 Changer InitializeDevice() failed - ERROR = 0x00000006 (ERROR_INVALID_HANDLE)
[4364] dd/mm/yyyy 11:34:59.482 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)
[4364] dd/mm/yyyy 11:35:05.739 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)

...

[4364] dd/mm/yyyy 11:54:15.019 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)
[4364] dd/mm/yyyy 11:54:20.051 ReadDeviceScsiInquiryInfo for "\\.\MediumChanger0" - failed - ERROR = 0x00000005 (ERROR_ACCESS_DENIED)
[4364] dd/mm/yyyy 11:54:25.083 Read Device Inquiries - end
[4364] dd/mm/yyyy 11:54:25.083 Serialize Devices:
[4364] dd/mm/yyyy 11:54:25.303 Device Discovery:

To resolve the issue remove the drivers ensuring the "Delete entries for tape devices that are not available" checkbox is checked, reboot the server, and reinstall the drivers as per the following article:

How to install and uninstall Tape Device Drivers using Tapeinst.exe utility
http://seer.entsupport.symantec.com/docs/243636.htm

This can be done from the Tools | Wizards | Device Configuration Wizard in Backup Exec, or by downloading the latest drivers.

Where to find a list of supported devices for Backup Exec for Windows Servers and the latest drivers for supported tape drives and robotic libraries
http://seer.entsupport.symantec.com/docs/251466.htm

Backup or utility jobs targeted to robotic tape library fails with the error "Parameter is invalid".
http://seer.entsupport.symantec.com/docs/307501.htm

The Backup Exec Job monitor shows ''Ready, No media servers are available'' for up to 14 minutes upon starting or rebooting a Backup Exec 10.x for Windows Servers media server.
http://seer.entsupport.symantec.com/docs/282316.htm

How to troubleshoot issues with a Robotic Library (autoloader/changer) or Tape Drive in Backup Exec for Windows Servers
http://seer.entsupport.symantec.com/docs/255501.htm

Backup jobs stay in the status "Ready, No media servers are available" in the Backup Exec Job Monitor
http://seer.entsupport.symantec.com/docs/294430.htm