I have upgraded to Movabltype 4.21. It was relatively painless but there was a small issue. I turned on the feeds feature and thought all was well. However when I published an entry the Save button resulted in…well, nothing. Upon further review I noticed that the mt-feed.cgi file was not marked as executable. I made all of the cgi files executeable but this one must have been added later. Everything seems to work now.

Now, I have to get used to the new interface.