Also had this problem on my 2010 2.0 D SE at 160,000mls. Local garage found a split air hose at the bottom of the engine, some 75mm dia and approx 150mm long with a slight kink in the middle. DPF became completely blocked. Hose replaced (cost over £50!) but local garage couldn't regen the dpf. Took it to local Subaru garage and they removed the dpf, had it ultrasonically cleaned and put back as new. They then did a forced regen (3000 rpm for 15minutes!) and the car was fine after. Now moved on to a 2015 2.5 petrol. New owner of the diesel has had recurrence of the problem at 190,000mls. Loved my 2.0 D SE but glad I moved to petrol. Also getting 45mpg on a run and 38mpg locally so quite happy with that.