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How to Fix the Installing Office Customization Error in Excel
Question details
The user needs to resolve an error prompt stating "Installing Office Customization" that appears when attempting to launch Microsoft Excel.
- Product
- Microsoft Excel
- Device & OS
- not provided
- Scenario
- Opening Microsoft Excel after installing or modifying third-party software such as ANSYS optiSLang.
- Observed behavior
- Excel fails to load normally and displays an "Installing Office Customization" error because it cannot locate the optiSLangExcelAddIn.vsto file associated with the ANSYS add-in.
Close all running instances of Microsoft Excel and note the exact name of the .vsto file mentioned in the error message before proceeding with the troubleshooting steps.
Start Excel in Safe Mode and Disable the Problematic Add-in
Running Excel in Safe Mode bypasses custom add-ins, allowing you to open the application and safely disable the missing or corrupted optiSLang add-in.
The 'Installing Office Customization' error is frequently triggered by third-party COM add-ins trying to load missing installation files, such as the optiSLangExcelAddIn.vsto file. Disabling the add-in stops Excel from searching for this file on startup.
Hold down the Ctrl key on your keyboard and double-click the Excel shortcut. Confirm that you want to start the application in Safe Mode when prompted.
Once Excel opens, click on the 'File' tab in the top-left corner, then select 'Options' at the very bottom of the left-hand menu.
In the Excel Options window, click on 'Add-ins'. At the bottom of the window, change the 'Manage' drop-down menu to 'COM Add-ins' and click the 'Go' button.
Find the 'ANSYS optiSLang' add-in in the list, uncheck the box next to it, and click 'OK'. Close and restart Excel normally to verify the fix.
Repair or Reinstall the Third-Party Component
If you actively use the ANSYS optiSLang integration, repairing its installation will restore the missing .vsto files necessary for the Excel add-in to function.
Use the Microsoft Support and Recovery Assistant
When manual add-in management fails or the add-in list appears empty, use Microsoft's official diagnostic tool to repair your Office installation automatically.
Experience Error-Free Spreadsheets with WPS Office
Avoid frustrating add-in errors and slow startup times by switching to WPS Office. It provides a highly compatible, lightweight, and completely free alternative to Microsoft Office, ensuring your spreadsheets open smoothly without heavy background customizations.
- 1. Download WPS Office: Visit the official WPS Office website and click the free download button.
- 2. Install the Suite: Run the quick installer to set up WPS Office on your device in minutes.
- 3. Open Your Spreadsheets: Double-click any Excel file to effortlessly edit it within WPS Spreadsheet without worrying about legacy add-in errors.
Frequently Asked Questions
Why do I get the 'Installing Office Customization' error every time I open Excel?
This error occurs when Excel tries to load a COM add-in (like optiSLangExcelAddIn.vsto) during startup, but the associated installation files are missing, moved, or corrupted.
What should I do if no add-ins are listed in Excel's Safe Mode?
If the COM Add-ins list is empty but the error persists, the customization might be forced via a corrupted registry key. You should use the Microsoft Support and Recovery Assistant (SaRA) or perform an online repair of your Office installation from the Control Panel.
Will uninstalling and reinstalling Office fix the customization error?
Uninstalling and reinstalling Office can reset registry keys and fix the issue, but it is recommended to first try removing the problematic add-in via Safe Mode or using the Microsoft Recovery Assistant to save time.
Can I manually delete the missing .vsto file mentioned in the error?
Since the error occurs because Excel cannot find the file, deleting it is not the solution. Instead, you need to tell Excel to stop looking for it by disabling the add-in, or restore the file by repairing the third-party software that originally installed it.
