Quote from Help Screen:
o NOTE: Whether the user intends to change any of the default fax setup information or not, each user must go into the Fax Setup function, enter the Fax Printer field once (by clicking on it, even if you don’t change the selected printer), and then click OK.

Users will be unable to fax documents prior to doing this.

Where is "Fax printer field" in Fax setup?