If the document type fields include a keyword list of FileDirector users (e.g. Approver), then the name entry in the keyword list must be an identical match to the Full Name property in the list of "Users and groups". The number of spaces must be identical, including any trailing spaces.

Hint: Check for unwanted trailing spaces after the name in the drop-down list.

You can force the check-in of the affected document and try to restart the process, as an administrator, by selecting the document and then clicking Undo Check-Out.