When Kronocard return an error 500 and the last try was about submitting cards online, one possible cause is that there is one or more images in C:\ProgramData\Kronozio\Images that have a oversized dimension. If the image is too large the call to the API is cancelled. When users are scanning at 600dpi I copy the files to my computer, resize them 50% using XNview and copy the image back to the client computer. Close Kronocard and restart the service.