If you see an error like the one below, then you will need to ensure a specific group right is enabled and that you belong to the respective group:
1) Refer to 'Group Rights'
2) Refer to the section 'Quote' and then 'Create Location in Quote'
3) Ensure you belong to any of the enabled groups in this grid
After this is completed, you will be able to add a billing address when the lead is RFQ'd.