Latvala tells in a Finnish interview http://www.sportti.com/uutinen.asp?CAT=1-2&ID=343465 about the Poland retirement:

Kaasupolkimen alle oli joutunut väärä esine. Yritin sitä kytkimellä korjata, mutta se sitten suli, koska ei kestänyt moottorin korkeita kierroksia.
Which translates to "a wrong object had gotten its way below the throttle pedal. I tried to fix it with the clutch but it burnt because it couldn't handle the high engine revs"

So after all it was a human error rather than a pure technical failure. Possibly the tool kit under the pedals like Lefebvre on the last day?