Thought I'd give a bit of an update if anyone is still following.
Replaced all injectors, still no good
Decided to run VANOS solenoid ABL again. I am not getting the error - Adjustment is too slow or the setpoint value cannot be reached. Quite odd as I have run this test before without the error.
I wonder if my new vanos solenoids are faulty, hmm. Seems to be occuring across all solenoids, perhaps an oil pressure issue. Will update as I discover more...