C# and Excel interop

One of my users is having an issue when trying to open an Excel file through my C# app.

Everything works ok when I run it from my machine and it works for other users. I am no Excel interop expert so hopefully you guys can help me out.

Here is how it is set up:

I added a reference to my app to Microsoft.Office.Interop.Excel.dll, version 10.0.4504.0 (which I believe is Excel 2002). On my machine I have installed Excel 2007. In my code I try to open a worksheet like so:

using Microsoft.Office.Interop
...
Microsoft.Office.Interop.Excel.ApplicationClass _excelApp = new Microsoft.Office.Interop.Excel.ApplicationClass();
Microsoft.Office.Interop.Excel.Workbook excelWorkbook = _excelApp.Workbooks.Open(workbookPath, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "", false, false, 0, true, false, false);
Microsoft.Office.Interop.Excel.Sheets excelSheets = excelWorkbook.Worksheets;
Microsoft.Office.Interop.Excel.Worksheet excelWorksheet = (Microsoft.Office.Interop.Excel.Worksheet)excelSheets.get_Item(1);

I logged the users version as Excel 9.0 (which is 2000). The error that the user gets is:

Exception='System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at Microsoft.Office.Interop.Excel.Workbooks.Open(String Filename, Object UpdateLinks, Object ReadOnly, Object Format, Object Password, Object WriteResPassword, Object IgnoreReadOnlyRecommended, Object Origin, Object Delimiter, Object Editable, Object Notify, Object Converter, Object AddToMru, Object Local, Object CorruptLoad)

It looks like the workbook cannot be opened. The file was confirmed to exist and was just loose on the user's PC at C:. I thought by using the PIA I wouldn't have to worry about Excel version issues. I know there are other users using Excel 2000, and it works on my development machine.