Could you please confirm the version of Acrobat/Reader installed on the machine?
Which Windows Operating System running on the machine-7/8/10?
Hi, we're using Reader DC Classic 2015.006.30279 on Windows 10 Anniversary 10.0.14393. The problem happens intermittently so it's difficult to isolate the cause. When the problem occurs, the user is prompted to enter the smart card PIN as normal but the 1400 error is returned and the document is not signed. Also, we're not using any 3rd party smart card middleware like ActivClient, just the built-in Windows middleware.
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Could you please try installing the update from the following link and see if that works?