After an update, last name needs to be added for the sender of a document. We are urgently working on a fix for this.
If you are having trouble right now to send a document or with an ongoing process, go to Account > User and add a last name.
It is now possible to start processes even if the initiator doesn't have a last name if you are using Scrive Classic. We are now working on enabling the same functionality in Scrive New.