As the user types in the box, explaining why their site should be reincluded in the Google index, the web page freezes and they get booted out. The issue seems to date back to July 26th, last Wednesday.
The issue was confirmed by Googler, Susan Moskwa on 7/28, saying, "thanks for letting us know, folks--we're looking into the issue." Then on Friday, Googler, Jonathan Simon chimed in saying, "We're still looking into this issue. In the mean time have you tried the potential workarounds that danielroofer suggests above?"
The form works fine for me, so maybe try deleting your cookies to see if that fixes things. If not, hopefully Google will figure it out.
Forum discussion at Google Webmaster Help.