I have Thunderbird 24.4.0 with Lightning 2.6.4 on a couple Windows 8.1 Pro w/ Media Center. Lately none of these computers will let me sync with my calendars that are on my iPhone. I have the direct url's to my calendars and they work for the first down load, but as soon as something get's updated to any event, task etc. Thunderbird won't download the new info, it simply says that the calendar is momentarily not available. I have the same info set up on a system running Ubuntu with Evolution mail & Calendar installed and it syncs just fine. So It's not my urls. How can this be fixed?