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When you post a file by using a file input element as described in RFC 1867 ("Form-based File Upload in HTML") to a Web page that requires Secure Sockets Layer (SSL) client authentication, Internet Explorer may stop responding (hang) after you select the client certificate to complete the SSL authentication.
Note that this problem does not occur if client authentication is completed before you post the file. This issue also does not occur with a "standard" form that does not use a file input.
This problem occurs because Urlmon.dll does not retry writing the content of the file to upload after the SSL client authentication has occurred.
To work around this problem, use one of the following methods:
Configure SSL client authentication on the form-based file upload page.
In the form-based file upload page, insert a hidden element (such as an image) that references an URL that requires SSL client authentication.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.