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Hello JohnPB1960,

Welcome to the Apple Support Communities. I understand you're receiving an error when you open iCloud for Windows.

It sounds like a good starting point would be to uninstall and then reinstall the iCloud for Windows app, using these steps from the resource titled Set up and use iCloud for Windows:

"Turn off or uninstall iCloud for Windows

If you turn off a service in iCloud for Windows, your information won't automatically stay up to date in iCloud, and you won't see updates made on your other devices. Follow these steps to turn off a service or iCloud:

• To turn off a service on your PC, Open iCloud for Windows, then select or deselect that service. To save your changes, click Apply. 
• To turn off iCloud for Windows, open iCloud for Windows, then sign out. 

If you want to uninstall iCloud for Windows, remember to make a copy of your iCloud data and save it on your PC. Then sign out of iCloud for Windows on your PC, and follow these steps:

Windows 8 or later:

1. Go to the Start screen, right-click in the bottom-left corner or click, then select Control Panel.
2. Click Uninstall a Program.
3. Click iCloud > Uninstall.
4. When asked to confirm, select Yes.

Windows 7:

1. Choose Start menu > Control Panel.
2. Click Programs > Program and Features.
3. Select iCloud > Uninstall.
4. Click OK to continue."

If you find the issue persists after you reinstall the software, this link has additional troubleshooting that may help: Get help using iCloud for Windows

I hope the above information helps to answer your question!

Cheers.