Excel generated error

There are 10 people accessing an Exel workbook. Each person has a tab in the workbook. The workbook is on a network resource. A folder within the Public folder on one of our servers. They are running Office 2000.
When two of the people open this Excel file this error message appears “Excel.exe has generated errors and will be closed by Windows. You will need to restart the programe. ” Any ideas would help.