For the weekend, I had been traveling and therefore had put Thunderbird 6.0 into offline mode. Today, I hooked up the netbook to the network, and asked Thunderbird to check for new email. It responded by noticing that it was still in offline mode, and asking me I wanted it to go online again. I confirmed, but nothing happened. According to "File/Offline", Thunderbird now even felt it was in online mode again, but no new email arrived. I had it check for email again, and once more I was told that Thunderbird still was in offline mode, and whether I wanted it to go online.
I tried a couple more times - often enough to feel pretty foolish about it. Then I created a new email message - and was greeted by a message box claiming that an unresponsive script was still running. I stopped the script (whatever that script may have been doing) - and now I could go online again.
Later I found that the problem is already described elsewhere, for example at http://www.thunderbird-mail.de/forum/viewtopic.php?f=31&t=54968.
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