I am trying to digitally sign an Excel spreadsheet. I can add the box, I can type my name at the X but when I click the 'Sign' button to complete the action I get an error message saying; "Your signature could not be added to the document. If your signature requires a smart card, ensure that your card reader is installed correctly" then can only click on the 'OK' icon and the dialogue box closes.
I had never gotten this error previously but now I cant sign any documents.