This is a common problem on CalCERTS: responsible designers cannot sign the CF-1R even though the correct designer name and designer company are chosen.
The registry needs something in the Designer's License field (highlighted above). You do not need a designer's license to sign as a designer, however.
If you do not have any relevant licenses, you may simply input "N/A" and Save Changes.
Having anything in the designer's license field will allow signatures to take place again.