I left my last job before getting a new one, as one of my Managers was impossible to work with, changing barriers all the time, being nice one day and not the next for no apparent reason.

However I need to go for interviews and they will ask "Why did you leave your last job!" Nobody goes for another job unless they are unhappy in their current one, but what is a good reason to give the interviewer?

I don't want to be negative against the company (as it was a good company to work for) or give the actual reason as I believe this would not help me get another job.

Any suggestions?