first thing to do is link the actuator pipe straight to the charge pipe, leaving the n75 plugged in. this will eliminate the n75 and you'll know if its the turbo or actuator creating your overboost? do you have a boost guage, it sould hold boost at 5psi without the n75.... so will feel very slow but if boost is still rising you could have a turbo or actuator issue, can check your actuator by clipping a cut up tyre valve into the actuator line and pumping it up to see if it holds pressure.
if its holding 5psi and not hitting soft limp/boost cut then your problem is likely n75 pipework (first thing to check really, and check properly all your vac hoses...) or n75... can buy cheap silicone hose on ebay and replace your vac lines for pennys, ones under the inlet manifold are crap, mine were anyway due to the common rocker cover gasket leaking oil all over them!
rosstechs website tells you all the possible causes for that code if you have a look...
i had the same code when i bought my car and it turned out a previous owner had fitted a chinese turbo, ko4 copy which i had to remove and send to bill at badger 5 for porting of the wastegate appature as they are often too small thus creating boost creep.
do you have a n249 delete? any other mods?