Weird error uploading file via https

[Jon Pincott]

Hello,

I've got a form that looks a bit like this :

<form action="https://my.server:8443/my/servlet" method="post" encoding="multipart/form-data">
<input type="file" name="myfile">
<input type="submit">
</form>

(i.e. a file upload form that submits to a servlet on another server via https.)

The problem is, I'm getting a "page not found" error. I think it's got something to do with certificates, because if you try to GET the servlet (e.g. browse to it directly), you are prompted to accept the certificate. If you try to POST to the servlet, i.e. using the form, then the certificate acceptance dialog does not display any you get a "Page not found" error.

However, if you change the input type from "file" to "text" and submit the form, the dialog box is displayed. So, what is it about using input type="file" that is preventing the certificate acceptance dialog from appearing, and how do I fix it?

Can anyone point me in the right direction?

Thanks,
Jon.

[Jon Pincott]

I've discovered this is a known problem with IE. One workaround is to include on the upload form a link to a resource (e.g. a gif) on the secure server. This allows you to accept the certificate before submitting the form.