How to pass parameters when to WebViewer from a form

Monma

using birt 2.2.2

I have a form such as:
<form id="foo" action="/WebViewer/preview" method="post" target="_self">
<input type="hidden" name="__report" value="/myreportdir/report1.rptdesign">
<input type="hidden" name="__format" value="html">
<input type="hidden" name="pTime" value="2010-02-12">
</form>

That I generate dynamically and submit using javascript to run a report. When I use the method "Get" (in the form) it works well (parameters are passed as query strings). But when I use the method post it does not work. And I need to use the post because of other parameters I will be adding later.

Am I not passing the parameters the right way when using Posts?

Thanks in advance for any help.

P.S: I am attaching the error I get when rasing the logging level to Finest