RESTORE VERIFYONLY is a good option to check SQL database backup after the backup has completed. It checks the backup to ensure it is complete and the entire backup is readable. The does not do an actual restore, but reads through the file to ensure that SQL Server can read it in the event that a restore using this backup needs to occur.
Personally, I know this error happens when 1. There is no directory with Log 2. There is not enough space on drive d:3. There is not enough permissions on d:\Log drive But actually The error was there because of the file was read only. May be there was already another backup file which existed in the folder with the same name and it was marked as read only. Due to the same reason, my backup was failing. Once I removed the checkbox for reading only, the backup was successful.