Last week Windows Live Sync was taken offline to fix a “serious problem in Windows Live Sync that could cause problems in rare cases for people who used Windows Easy Transfer”, according to Eric Doerr on the Windows Live Sync blog.  Even though it’s caused some users to get a little grumpy about having to reconfigure, the upgrade and the resulting reconfiguration are necessary:

If your computer was already running Windows 7 before this update, you’ll have to go to the Sync website to add your computer back to all the folders you’re syncing. We know this is a hassle and we apologize for this inconvenience. You’ll also see that your computer shows up on the Sync website with a new name—you can safely go ahead and delete the old computer from the website. Rest assured that your files and folders are safe.

We found this problem in Sync through internal testing, and although it was very rare, keeping your data safe is our highest priority. We wanted to be absolutely sure that this problem wouldn’t happen to anyone.

Windows Live Sync should force an upgrade before you are able to use it, or you can try it out at http://sync.live.com.  After logging in with a Windows Live ID, you’ll be able to download the latest version (14.0.8089.0726), or install it on your Mac (although we’re pretty sure it still doesn’t work with Snow Leopard, judging by the comments on the blog post).