Hopefully you have a reference to a coworker were you just left. It is better than no reference and will more than likely fillin the gaps in the story if someone calls. With that said, no one calls references these days. I have been listed for years as a reference and the few that do call me are just 'calling to check references' not usually interested in learning anything. The last guY that called had names confused and gave my name as the person applying for the job! Don't stress over it. Stay positive in the interview and good luck!
I would second this one, most companies are so worried about liability that they instruct managers to only give confirmation of name and dates of employment. Giving a reference does not benefit the former company, but could leave them liable as such most see it as a loosing proposition to allow references.