Underscores are not good to use in URLs as search engines do not treat it as a space or delimiter. So Snow_Bee would be considered Snowbee. I believe search engines have gotten better at figuring out when a word like this should be two words, but the best practice for this is to use hyphens (e.g. Snow-Bee).
Here is a video from Matt Cutts about it:
http://www.youtube.com/watch?feature=player_embedded&v=AQcSFsQyct8
This wouldn't cause you to drop off though especially if you ranked previously. Is it just for this one term or is it for multiple terms? I would be looking at link backgrounds to be sure there weren't any spammy links getting devalued that maybe didn't get caught before, or perhaps review the content of the page to see if it might have gotten caught by the penguin anti-spamminess updates.