What is this residue in bottle of bitters?

I've only used this bottle of bitters a handful of times and only noticed it today. Can't find anyone else with this problem. The bottle was kept in the dark at room temperature. Is this normal? Should I toss it?Edit:Pics http://www.reddit.com/r/cocktails/comments/3eqa7n/what_is_this_residue_in_bottle_of_bitters/