Has anything else changed on the machine or did the data sources receive some sort of update? Did any new drivers recently update on the computer?
Does rebuilding the flow allow for the extract to be created and the flow run?
Please also make sure the latest version of Tableau Prep is being used as the development team is constantly updating Tableau Prep. The latest version has several fixes included.
Hope this helps!
Nothing has changed. IT is quite erratic. Sometimes I am lucky when I do a complete reboot. Now it seems to be working fine.