I have this problem many times when I'm futzing around with themer themes and get the force close error. The way I've fixed it, and it works every time, is to go into the apps section of your android settings, find themer and clear the defaults and the cach. Close settings and open themer. It goes through the setup process like it does the first time you open it. Then, I go into my folders and delete the offending theme that caused it so it won't show up in my exported list of themes I can choose from within the app.
I get all themes that don't come included with Themer from mycolorscreen (not intended as an advertisement) and sometimes, I think the coding or whatever term you use, is frigged up because this is the only time I EVER get that force close. I use Themer constantly and nothing else gives me the force close.
I hope my experience helps.
Ron