Thanks, that fixed the pair of errors that were showing up in my Event Log every half hour.
My problem still exists, and I have some more detail about it...
First, there are no errors in my Event Log when this issue comes up.
Secondly, other forms on the site also fail when this issue arises. When I'm logged in as Host admin trying to update pages and the issue arises, my simple forms for collecting user data also fail. They simply return the same page as if I had never submitted the form. This seems to hold true for all Postback links as well.
Clearing my browser's cache and cookies does not seem to help. I can login to the site from an entirely new computer and the problem will persist. Today when it came up, I rebooted IIS and closed all of my browser windows and it went away. In the past rebooting IIS has not solved the issue, rather it will simply go away on its own after a few hours or overnight.
Is there some other way I can investigate this while it's occuring? I was wondering if an incomplete page load could be causing HTML forms to be incomplete and thus run into each other. But due to the complexity of the postback mechanism across a large page, this sounds like a huge hassle for such a blind guess.
Has anyone else experienced this problem?