Unknown error System Information CGetSigningParams-4043

I have a document that requires a digital signature, as soon as the field is clicked a dialog opens that lets me select the signature I want to use. I've used this digital signature many times without error before.

Now when I select the signature I receive this error:

I then cliek OK and this dialog appears:

I've deleted and recrewated the signature but still receive the same error.

Can anyone point me to some documentation that defines what CGetSigningParams-4043 is and how to resolve it?

Thanks.