I had Thunderbird and switched to Outlook when I purchased Office. I liked Thunderbird better so I switched back. I exported my Outlook calendar and imported it to Thunderbird. The calendar works, no problem. The problem is that when I open Thunderbird and select the calendar for the first time Thunderbird hangs. If I check the message indicates that Thunderbird is busy. After a period of time everything works. The only time this occurs is when I start Thunderbird and select the calendar for the first time. Can you tell me why? If it makes any difference when I imported the calendar I did not realize how Thunderbird worked and I imported it creating a new calendar with the name of the imported file. I had a Home calendar with nothing in it and my imported calendar. I decided to export the calendar that was created during the import. I then imported that file to the Home calendar and deleted the original imported calendar.