As a general rule, honey does not spoil and is one of the best "naturally preserved" foods on the planet. Of course, there is always a caveat. There ARE small amounts on natural yeasts in honey. If the honey had to much of a moisture content, it could ferment. This could be aggravated by leaving containers open as they will draw moisture from the air.
To specifically answer your question, if your yeast tastes spoiled (sour) then it may be partially fermented. The natural yeasts are of such a low tolerance that there is plenty of convertible sugars remaining. While I personally do not boil my honey prior to fermentation, that is an option. Regardless, my personal opinion is that any quality yeast strain will not have a problem gaining control of a must in which a natural yeast strain is present.
Hope that was not too long on an answer, let me know if you have any other questions.
Cheers