HTTP POST doesn't work on Internet Explorer 8 (after redirection)

I'm trying to redirect a domain to another site, without changing the first URL (users should keep viewing http://www.myurl.org since the new URL would be https://wwws.enterprisedomain.com).

I could do this, inserting a frame in the index.htm of the first domain (I know it's not the best practice, but it worked well for now):

<frame name="main" src="https://wwws.enterprisedomain.com">

The fact is that https://wwws.enterprisedomain.com has a login mechanism in ASP.NET. It's OK on Firefox and Chrome, but when we use Internet Explorer 8, it seems that POST doesn't work!

Why hide the user is working securely?

I think you're trying a solve a problem that doesn't exist, take a look at this excellent library which will direct users to the correct protocol (HTTP or HTTPS) regardless of what they type in. So a user who is used to going to http://myurl.org will automatically be directed to https://myurl.org without them doing a thing.

Forget the frame idea.