iCloud Calendar isn't syncing and iCloud Control Panel won't open (Runtime Error).(on HP HDX 16 with Vista Ultimate) That is followed by message saying PhotoStream has stopped. I'm just confused at this point. Do I need to uninstall/reinstall something?
Not sure if it will solve your problem but you could try uninstalling the iCloud control panel for windows (search for iCloud in uninstall or change a program), then reinstall the latest version: http://support.apple.com/kb/DL1455.