I am 99% sure I know the cause of this. When the AWB reading is somehow saturated by an extra bright light source at the time when the AWB is set, then the WB reading is way green. It's happened to me with many other cameras, but actually, with my 5D Mark III it hasn't happened yet. The same thing can happen if you try to set manual white balance from a very overexposed shot, with at least one of the color channels completely saturated.
A picture turning green can't possibly have anything to do with a memory card error, unless the card error somehow has an intelligence of its own and knows how to change the picture's color rather than randomly corrupting some bits.
5DIII, 5DII, 7D x5, 6D, T2i, T3, 1D X, 10-22mm, 16-35mm II, 18-55mm II, 18-135mm IS x2, 70-200mm f/2.8L II, 24mm f/1.4L II, 50mm f/1.4, 50mm 1/1.8 II x2, 85mm f/1.8 x2, 100mm f/2 x2, 135mm f/2L x2, 200mm f/2.8L II x2, 1.4X III, 2.0X II, 60mm f/2.8 Macro, etc. only had room to list a few Canon items