If you end up in a state where you can no longer double-click in the Windows Explorer on .sky or .skyd files and have Skyline open the files for you, do the following:

• Run regedit.exe and delete the following keys if any are present (they may not all be)
• Delete the keys HKEY_CLASSES_ROOT\.sky and HKEY_CLASSES_ROOT\.skyd
• Delete the keys HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.sky and .skyd
• Delete the keys HKEY_CLASSES_ROOT\Skyline.Data.0 and HKEY_CLASSES_ROOT\Skyline.Document.0
• Reboot your computer
• Wait for an update or reinstall Skyline (see also Recovering From a Broken Installation)

Thanks to Stack Overflow for this entry:

https://stackoverflow.com/questions/6489112/clickonce-deployment-file-association-not-registering