We have had rare reports of a couple issues when uploading standings using PDF's or generating PDF's from the Print Preview screen.
We've identified an issue with a library used to generate the PDF and reported the issue.
With the help of some customers, we believe we've identified the issue to be with the Standing Sheet Messages.
Try removing the messages from your standings to see if you can successfully upload / generate PDF. If successful, put back the messages and clear the messages of content and then retype (do not copy and paste) the content. If successful, then great. If not, then look for any special characters used and try removing.
We hope to have a resolution with the library itself soon.