Managed to solve this. For reference, the account that the scheduled task was running under (scv_tableau) did not have any proxy exceptions set (in IE connection details). I had previously checked this and it seemed ok BUT i was using my own account when i checked the proxy details. When I logged into the server using the account "scv_tableau" the propxy details they were empty.
All I needed to do is to copy the proxy details from my account to the svc_tableau account
Nice John, thanks for sharing the answer! Glad you got it working.