Pid=1452 Exeption number:C0000005

Our Accountant keeps getting the Access Violation error when he’s doing the payroll. He’s pulling information from an Excel Spreadsheet. He has a Windows 2000 OS and the error in the error log is as follows:
App:pid=1452)
Exception number: c0000005 (access violation).
He then has to restart and then it works all fine after the restart.
Why is this happening and what can we do to avoid the error?