Event ID #560 Error Message

We have a database at a network location that we allow many of our employee's to access. They all have the same settings however a few of them return a Failure Audit in System event viewer log occasionally. It is not every time they access the database. Below is a copy of the details. Any ideas what could be causing this?

8/5/97 8:11:45 PM Security Failure Audit
Object Access 560
<USERNAME>
<MACHINE NAME>
Object Open:
Object Server: Security
Object Type: File
Object Name: <FILE PATHNAME>
New Handle ID: -
Operation ID: {0,1163459588}
Process ID: 8
Primary User Name: <USERNAME>
Primary Domain: <DOMAIN NAME>
Primary Logon ID: (0x0,0x2EA46)
Client User Name: <USERNAME>
Client Domain: <DOMAIN NAME>
Client Logon ID: (0x0,0x4544E865)
Accesses READ_CONTROL
ReadData (or ListDirectory)
WriteData (or AddFile)
AppendData (or AddSubdirectory or CreatePipeInstance)
ReadEA
WriteEA
ReadAttributes
WriteAttributes

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