2 possible issues immediately come to mind.
First is Floor Loading, every aircraft has a maximum floor loading which is typically displayed in the POH and is shown as a lb/square inch or square foot figure. If your not familiar basically if you were to get say 300kg of freight onboard an aircraft thats evenly distribute over a foot of area on the floor then its 300kg/ square foot which may be ok, if you then go that same weight but it only took up half a square foot you would effectively double this figure which the floor may not be able to take, this could be the potential issue. Not sure where you'd find this info for the Warrior, I know its in the Weight and Balance section in a 206 manual and is in there as a Note.
The second possibility is the seat itself. Some aircraft have specific weight limitations on the Seat, the Airvan for instance is something like 140kg (Don't quote me, I don't fly the things!). Therefore this may also be the issue.