You are flowing the max amount of air the MAF can read. Any more than this comes up as an error. Either fit MAF into a bigger housing and rescale (I dont know how to rescale) or fit a higher rated MAF from something else and again rescale or whatever needs to be done.
Personally I would like to convert to speed density (MAP) and do away with it alltogether. But thats just me, and I dont know how to do that yet either...
I just told my mate who owns the car to turn down the boost and deal with it as I am doing everything for free for him so far and spare time is valuable to me right now
oh, and Subaru's store history fault codes too which is nice, so even if the fault isn't there anymore it still keeps the code and marks it somehow as "history" as well as the other current codes as per normal.