If you're getting ODBC errors form a site when you synthesize a form POST, then that site's code is... brittle. It kind of looks like they may be building a query from fields passed by form. At best, a security problem waiting to happen.

Two things jump out form your code. First, you are passing an anonymous hash to POST rather than an anonymous array. The HTTP::Request::Common POD shows anonymous arrays (as do the example in the Perl Cookbook), so try that. I suspect you aren't creating the HTTP POST that you think you are.

The other is that you're not checking $request->is_success after your first post. That might be worth doing.