Hi,
I/O errors occur also due to delays in communication between the tape device and Backup Exec.
1. http://support.veritas.com/docs/191158 is very helpful to check the settings on your SCSI Controller.
2. Its recommended to not attach the tape device to a RAID Controller, except for tape devices that are certified by the OEM's to be compatible with RAID Controllers. Use a separate SCSI Controller for your tape device.
Additional tip:
You might want to check if there are any hard/soft write or read errors on the media -- click on Media in Backup Exec > Select a media that was used for a backup which failed & view Media Statistics down below in that window. Hard errors may mean that the media is bad. You can try a new tape. Also clean the drive 3-4 times consecutively.
Have a nice day!
NOTE : If we do not receive your intimation within two business days, this post would be "assumed answered" and archived.