Help needed - the female

Hello, I need some advise from the fairer sex...I work with a gorgeous brunette and we have been chatting to over the last couple months, I have mentioned going out for a drink a few times in idle chat when we have seen each other around the office, and she has been kinda receptive, but nothing firm eventuated.
Recently I had the opportunity to ask her out formally as we both wanted to catchup on happenings at work - in particular I had a role she was interested in. So we exchanged emails and she was really receptive and a date was set. The day arrived and she advised that she was unable to go that evening apologising and asking to reschedule, which we did - again quite receptive to catching up.
The second date arrived and she again let me down - emailing me that she was not interested in the job; further she was not up for a drink and that she preferred to go straight home after work as she had a long commute. Needless to say I was left a little confused! No idea for the reason for the sudden coolness and change of mind (it is a woman's prerogative I know!) as I have said nothing to anyone that I work with that we were even catching up outside of work, nor have I come across too strong.
Being the consummate gentleman, I responded and said that was fine. Since then, I have avoided contact . However I would appreciate a woman's option - WTF happened and how should I manage?...answers on a postcard please...!

perhaps she has a boyfriend that expects her home at a specific time. try a lunch date rather than after work.

easiest and best solution is to ask her why she is avoiding you since she canceled two outside evening business meetings and changed her mind about being interested in the new job. direct approach is always best with women.