Rehearsal dinner hardship

I've been searching high and low for my rehearsal dress, and I have yet to find something. I originally ordered this cute little number from JCrew, on sale for $78.
But this is a summer dress. The fabric and style screams summer, and well my wedding is not in summer, it's actually at the tail end of dinner.

I do have a dress sitting in my closet, worn once at a friend's bachelorette party in Vegas in June 2008. Here I am with the dress. I actually love the dress a lot, I've just never had the occasion to wear it again.
Why am I having such a hard time with the rehearsal outfit?