The most common reason why signing fails, is the ‘Token signing’ extension on your internet browser. It needs to be ‘Enabled’ or ‘On’ as in the newest Chrome browser.
When using Chrome - Double-check if you have the extension called ‘Token signing’ available and enabled (‘On’). You can find it from the upper right corner Chrome menu by clicking on ‘Extensions’.
When using Firefox - Double-check if you have the two required extensions called ‘Token signing’ and ‘Firefox PKCS11 loader’ listed and in ‘Enabled’ status. You can find them from the upper right corner menu by clicking ‘Add-ons’, then ‘Extensions’.
After changing the status of the ‘Token signing’ extension, you'll need to restart your browser by closing all tabs/windows of the browser and removing the card reader.