You receive an error message when you attempt to save or open a file in Excel 2000

When you attempt to save or open a file in Microsoft Excel, you may receive one or more error messages similar to the following:

• Excel caused an invalid page fault in module MSO9.DLL at memory address.
• C:\Program Files\Microsoft Office\Office\EXCEL.EXE
  A device attached to the system is not functioning.
• The C:\PROGRAM FILES\MICROSOFT OFFICE\OFFICE\MSO9.DLL file appears to be corrupt. Reinstall the file, and then try again.

This behavior can occur if the Mso9.dll file is damaged (corrupted).

To resolve this issue, rename the Mso9.dll file, and then use Add/Remove Programs to repair Excel.

Rename the Mso9.dll File

1. On a Microsoft Windows 95 or Microsoft Windows 98-based computer, click Start, point to Find, and then click Files or Folders.
   
   On a Microsoft Windows Millennium Edition (Me)-based computer, click Start, point to Search, and then click For Files or Folders.
2. In Windows 95 or Windows 98, type Mso9.dll in the Named box. To ensure that the entire hard disk is being searched, select My Computer in the Look In box. Click to select the Include Subfolders check box, and then click Find Now.
   
   In Windows Me, type Mso9.dll in the Search for files for folders named box. To ensure that the entire hard disk is being searched, select My Computer in the Look In box, and then click Search Now.
3. Right-click the file, and then click Rename. Rename the file by changing its file-name extension to .old, and then press ENTER.
4. Close the Find Files dialog box.

Repair Excel

1. Click Start, point to Settings, and click Control Panel.
2. In Control Panel, double-click Add/Remove Programs.NOTE: Because there are several versions of Microsoft Windows, the following steps may be different on your computer. If they are, see your product documentation to complete these steps.
   
   
3. On the Install/Uninstall tab, click either Microsoft Excel or Microsoft Office, depending on how you installed Excel.
4. Click Add/Remove.
5. After Setup begins, click Repair Office.
6. Click Repair errors in my Office 2000 installation, and then click Finish.

The repair process may take several minutes while Office Setup repairs any damaged or missing files. If you receive a message to restart your computer, click Yes.