500 server error on subtheme settings

I was working on my subtheme and wanted to turn off the wireframe setting, but when I go to http://whatever.com/admin/appearance/settings/myTheme, I get a 500 server error. Any idea what could cause this? I did quite a bit of work over the past few days and haven't encountered errors anywhere else, but I can't say whether or not this happened "suddenly" as I've done quite a bit of work since I visited that specific settings page. I can't see anything unusual/different about key files like myTheme.info or template.php off the top of my head. I cleared all cached data without result and am not sure what else to suspect or try.