It's telling me I've already made the post. It ONLY happens at work so I assume it something to do with the proxy, works fine at home on the same PC.
I get that problem from time to time. I never knew what was causing it. But the only times I've ever had that problem is when there was something wrong with D.net, such as the recent server death that happened.
When that happens, hit the back button, copy everything that you posted (most times everything you wrote is still there), and then just kill IE, reload it, go back to the thread you were gonna post in, post a new reply, and paste everything into it.
Works for me.