I had previously extracted "visitorId" from Data Warehouse API 1.4 but I am unable to do so using Reporting API 1.4-it gives the error "Element combination not supported". Is this element not available for extraction in Reporting API 1.4?
DWH contains a separate column called visitorID that's why when you use source as warehouse it works but normal API does not have any such column. If you check in workspace or R&A there is no such out of the box column available which capture the visitor ID by default hence it throws an error.
If you want to pull visitor ID from normal API 1.4 without using source: warehouse, you would need to capture the visitor IDs in a custom dimension(evar/prop) and fetch data for that variable.