Error _xldudf_ in your formulas

If you're using Excel and encounter issues where custom AI functions like "ChatGPT for Excel" are not recognized, leading to an _xldudf_  error in your formulas, it indicates that Excel is unable to link the names to the custom functions. This is often due to the custom functions portion not loading correctly. Here's a simple troubleshooting guide to help you get back on track.

Step 1: Test in a New Document

1. Open a New Document:
   • Start by opening a new, empty Excel worksheet.
2. Run a Custom Function:
   • Activate the "ChatGPT for Excel" Add-in.
   • Try running a custom function to see if it's recognized. For example, type in a cell =AI.ASK("Explain climate change") .
3. Check Results:
   • If the function works in a new worksheet, return to your original worksheet.
   • Manually correct any function showing as =_xldudf_  by changing it to the correct format, such as=AI.ASK("Explain climate change") .

Step 2: Re-Install the Add-in (If Necessary)

If custom functions don't work in a new document, it suggests the add-in installation might be the issue. Follow these steps to reinstall:

1. Uninstall the Add-in:
   • Follow the guide How to remove an Excel Add-in on Windows for removal instructions.
2. Restart Excel:
   • Close and then reopen Excel to ensure a clean state.
3. Reinstall the Add-in:
   • Install "ChatGPT for Excel" from Microsoft AppSource.

Post-Installation: Restoring Premium Subscription

After reinstallation, if "ChatGPT for Excel" reverts to the free version, you may need to restore your premium subscription:

Follow the guide How to Restore Your Purchase