Eli Bendersky's website Since Windows sounded its yearly death bell and I reformatted and reinstalled it on Saturday, I've been observing some very peculiar behavior of Internet access. I couldn't write in some forums, couldn't upload FTP files, and most weird of all, couldn't update some options in this blog (WP administration).
Now, this is really weird because all option updates are just DB writes. I even went as far as pouring over the PHP code of the options page and downloading the wp_options table from the DB. No clue why some options work and some don't.
Anna suggested it might be MTU problems again... and was absolutely right ! This time I updated the MTU locally on my PC and not on the router, using a freeware utility called TCPOptimizer. Set it to 1400 instead of 1500, and everything works.