Completed status: Failed 0xe0008488 - Access is denied. Exchange 2007

Hello Experts,

I have a backup job that sometimes backs up successfully and sometimes it doesn't. I have a Backup Exec 11d taking a disk-to-disk Exchange 2007 snapshot every night.

Some nights the backup job successfully completes. Without any changes to both servers (i.e. Windows Updates or setting changes), the same job would produce a:

Completed status: Failed
Final error: 0xe0008488 - Access is denied.
Final error category: Security Errors

For additional information regarding this error refer to link V-79-57344-33928

Backup- \\Exchange2007\Microsoft Information Store\First Storage Group
Unable to complete the operation for the selected resource using the specified options.  The following error was returned when opening the Exchange Database file:  '-1018 There is a checksum error on a database page. '

I'm trying to figure out why sometimes this job completes and sometimes it fails...when it fails, the byte count is the same as a completed job. Can any give me more insight to why this may be happening?