I gave up on automatic updating a long time ago because WordPress could never log into my FTP account. I tried it again after reading your post using a non-root account, and it was successful. However, I got the same error messages you did when trying to upgrade from Tweet This 1.5.2 to 1.5.3, and it didn't work on the third try either. I had to wait five minutes before the error message would show up each time I tried upgrading.
I have no idea how the auto-upgrade works or what is causing this. I'll do some research on it tomorrow, and I'll try using FTP instead of FTPS. If anyone else can shed some light on this, please post.
Tweet This has been downloaded 32,000 times and no one has reported this before. I hope it doesn't affect everyone.