How long have they been incubating?
It doesn't look good but I would continue to incubate it until I was sure but put it carefully in a separate container..
The air around them could be too moist. Eggs are very picky and they have to be just right to be good eggs. I agree with @kinyonga to put them in a separate container with a little bit drier air. The egg may be a little less tolerant than the other eggs.
We humans are inquisitive creatures that do a lot of touching! The more we open and mess with the eggs the worse the hatch rate gets. By handeling the eggs we remove some of the natural antibacterial/antifungal stuff that is on the eggs when they are layed. I have on occasion seen mold forming on my eggs but never slime. I would have to venture on the thaught that the slime is feeding on the egg and also preventing oxygen to diffuse in to the egg. I think it is in the best interest of the good egg to be removed from that container. Wash your hands very well first! Do not touch the other egg first. You can also take some foot fungus powder and sprinkle a very small amount powder around it and close to it but preferably not on it. Best of luck!