Forum OpenACS Q&A: Response to ns_returnredirect breaks with nsvhr and IE?

I bet the reason that piece of code is causing this problem is
because of what Jerry said about IE trying POST but then trying a
GET instead.  If that's so then you should receive a similar error
when accessing the target page from a browser without passing it a
query string or POSTing to it.

Are you redirecting the target of a POST?