I'd say that was just mold and/or yeast growing on the surface. In the anaerobic environment down in the brine, the sauerkraut is probably just fine. Undesirable aerobic organisms are why fermenting containers with air locks make fermentation so much easier. The first week of fermentation produces enough CO2 to completely purge the container of oxygen, and no yeasts/molds/fuzzies can grow.

And, you don't even need fancy air lock containers to do this. I make my kraut in ordinary canning jars with metal lids (making sure that the lids are new enough that the rubber seal is still soft.) My recipe is a half tablespoon salt per pound of shredded cabbage. I pack it into quart, wide-mouth jars, weigh the kraut down with little ceramic weights made for that purpose, and seal the jar tight (making sure that there is no stuff between the lid and jar.) Once a day, for the first week or so, I loosen the lid just enough for the built up gas pressure to escape with a hiss and then re-tighten the lid. After ten days to two weeks at room temp, I put the jars in the fridge to age for a month or more.

From what I have read, the top layer does develop a mold, but the rest should be fine... http://www.wildfermentation.com/resources.php?page=sauerkraut Step 8 they mention that the mold/scum is normal just discard when ready to consume

Carefully remove the top layer, scrape off the mold and wipe the upper surface of the container. Then dump the kraut into a large ceramic bowl and pick through it to remove any more mold. Put the juice through the strainer and put everything back and smash it down again. It should be fine. The key to making non-fancy sauerkraut is to disturb the top EVERY SINGLE DAY, and try to keep it below 65 degrees. I have gotten wonderful kraut even with heavy top and side mold. The only time I have had to throw it away is when I failed to control the temperature.

My family has been making kraut in giant crocks in the basement for my entire life (slightly over half a century). I'm pretty sure the skim the top often (if not daily). I'll check.

I got one ruined batch once. I've since gotten a set of cheap airs lock from here: http://www.amazon.com/Piece-Plastic-Airlock-Sold-sets/dp/B000E60G2W/

I then punched a small hole in the lid of a wide mouth jar (had ghee in it before, all metal lid, so no BPA lining) and used gum to seal it.

I also found that using lots of salt between each layer of sliced cabbage, pack the jar all the way to the top, and then adding some water at the end, maybe half way up the jar helps kick start the fermentation.

Last batch, I also threw in some beets.

Be sure to fill water to the fill line of the air-lock as this is what keeps air out. As the bacteria ferment and produce CO2 and other gases, the gas bubbles up through the air lock water and escapes, keeping the internal pressure the same.

Doing it this way doesn't require a special expensive ceramic pot, nor weights, and is dirt cheap.

If it smells good, I'd say take a small bite, making sure to spit it out if it tastes bad in any way, and then wait and see how you feel. If the next day you feel ok, try a larger bite. Do it for SCIENCE.