Looking at that article it would seem as though an extreme consumption of protein was taken. Too much consumption of anything including normal water can kill you.
The BBC did an interesting documentary not too long ago and it seemed the main negative was wether it actually works and if you could actually get just as much protein through food in a less expensive way.
The other negative was an individual who believed his high intake of protein powders caused him in his early 20's to generate kidney stones. This point maybe be of particular interest to crew in a pressurised cabin due to the low humidity.
I was more interested if anyone new if off the shelf protein powders could cause any issues relating to blood/urine tests for medical renewals etc.