I still have not resolved this issue, although it hasn't occured for a while either.
I havn't discounted that it could be sticking Vein mechanisim, a sticking mechanisim could cause the viens to move much more slowly than they should.
I also plan to replace the vac pipe as it is a cheap thing to do, an a small split of hole could cause the VGT actuator not to engage the geometry in time to alter the boost pressure before a fault is recognised by the ECU.
To summarise, dirty/obstructed VGT mech or slightly leaking vac pipe of even faulty vacuum solenoid could cause the system to respond slowly and the boost pressure to reach a level that the ECU determines is unhealthy.
I belive the VGT solenoid valve has a small foam air filter, would also be advisable to check all electrical connections. on the following MAF, VGT solenoid.
I have also heard MAP and possibly exhaust recirculation valve can cause issues.