I have been using WordPress 2.7.1 for a few months. In the very beginning of the first two months, I was able to upgrade the plugin, with some chances of failure. But lately, I was totally unable to upgrade the plugin in WordPress through built-in FTP. It just failed miserably, with the message: Download failed.: name lookup timed out.
As this problem has been happening with the chance of 100%, I suspect that this might be the problem from Web Host side, probably caused by incorrect setup or configuration. Until today I googled the problem, I eventually found a working solution, thanks and redirect by CarltonBale to WordPress Trac.
Here is the detailed solution of mine:
And finally, plugins updates is working. Going to reduce the growing number beside Plugins tab 🙂