The other day I had a few extra USB devices to plug in my main rig. Suddenly start getting the message "Not enough USB resources". So counting up I had 12 connections and a couple of ad hoc ones (phone / tablets etc.). Didn't think this was a lot but it turns out to be an issue with xHCI, switching to EHCI in the BIOS fixed things.
Thought I'd share
Thought I'd share