Hi there!

It sounds like you're having trouble opening xlsx files with Excel Viewer 2003. Here are a few things you can try to resolve the issue:

1. Make sure you have the latest version of Excel Viewer 2003 installed. You can download it from the Microsoft website.
2. Check if the file you're trying to open is corrupted. Try opening a different xlsx file to see if the issue persists.
3. Try repairing the Office Capability Pack. To do this, go to Control Panel Programs and Features Microsoft Office Compatibility Pack Change Repair.
4. If none of the above solutions work, you may need to uninstall and reinstall both Excel Viewer 2003 and the Office Capability Pack.

I hope one of these solutions works for you.