We have 14-15 databases that get transaction log backups every 1/2 hour. They are backed up to a local drive - not C:/, but the same drive the data files are on. Each database has its own backup folder. All's been well for 9+ months, but in the last week or two we're getting failures:
Executing the query "BACKUP LOG [xxxx] TO DISK = N'F:\\MSSQL.1\\MSSQL\\Backup\\xxxx\\xxxx_backup_201205140830.trn' WITH NOFORMAT, NOINIT, NAME = N'xxxx_backup_20120514083001', SKIP, REWIND, NOUNLOAD, STATS = 10" failed with the following error: "Cannot open backup device 'F:\\MSSQL.1\\MSSQL\\Backup\\xxxx\\xxxx_backup_201205140830.trn'. Operating system error 5(Access is denied.).
BACKUP LOG is terminating abnormally.". Possible failure reasons: Problems with the query, "ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.
When this happens, there'll be a zero byte file created in the directory. The backup 1/2 hour before and 1/2 hour after will go just fine. The specific database that fails is random - not always the same one(s). Some days none will fail, some days 3 or 4 will fail over the entire day. I've never seen two different databases fail at the same time, or the same one fail twice in a row. Not running especially tight on disk space. Server was rebooted for a third-party application update, still seeing failures.
Been Googling but no concrete answers. Where should I look next?