'an unexpected error occurred'

After numerous attempts and tweaks, I finally got 'Windows Fax & Scan' in Win8.1 to say 'sending page1', only to follow it with 'an unexpected error occurred'. I had made sure that the fax was the ONLY (and first) connection to my phone line. The fax was a USB. The recipient fax was on and active. What can I do to get my fax received at its destination ?