You can take a look at this example:
A few things to consider is whether you are URL encoding the data you are posting or not. If the values of the variables sent, are non alphanumeric, you will have to URL-encode them.
Also try to remove or change (if you are not already doing it) the content-type header to something like this:
One way to debug your problem, is to get the response code from the server by calling the getResponseCode() method on your http connection, in order to see what kind of problem the server encountered.
Also compile your code with the appropriate Nokia SDK, in your case Nokia's 5th edition SDK.