One area where you may find this error is when "consuming a service which requires a private certificate that is missing from the keystore", as I had found in an internal support case when searching for an answer to this community question. In such a scenario, you may also see "<key alias> in UNRECOGNIZED" in the "Select Private Key" dialogue box.
In another case, it was supposedly resolved with an ncipher firmware update, so applying that may also do the trick if you use ncipher. I would start with the first one mentioned though, as that's likely the most accurate answer for your environment.