I'm going to guess here... we see folks unable to post from certain corporate networks that run paranoid software that blocks traffic that looks malicious. Things like SQL in particular tend to set those off.
One workaround is to visit the site over HTTPS, which makes this sort of traffic monitoring impossible.
Since you were able to post from another network and there don't seem to be any related exceptions in our logs, my money is on that. If you run into this problem again from that same location, try the workaround above and let me know if it works.