Sounds like it could be the vinegar fly. The bucket for the first fermentation has to be kept well covered with several layers of muslin cloth. Even better if you can secure it with a string or rubber band.
The other thing that keeps problems to a minimum is to rinse all utensils out with boiling water from the kettle before using them.
Hope this helps.
Ian - Pagan Editor
"We can never obtain peace in the outer world until we make peace with ourselves."
"With realization of one's own potential and self-confidence in one's ability, one can build a better world. "