If you see black or blue-green mould in the bin, this means that your waste is rotting instead of fermenting.
Bury your rotting waste in at least 10cm of soil in the ground or a large pot of soil, wash the bin thoroughly, and start again!
To keep this from happening in the future, make sure you:
Close the lid tightly
Add enough enzyme spray
Tap out bokashi juice frequently
Keep the bin in a relatively cool area