I’m getting that as well though I had it with other themes I was testing too.
It seems to take exception to pngs (a lot of jpeg images worked) though the images smaller than 300px square all worked fine regardless of file extension.
I had a look around the wp support and found this
http://jonrwilson.com/2009/12/wordpress-http-error-crunching-htaccess/
I’ve not got round to trying it yet, but it’s something I will be trying.
Out of your list of plugins I only have jetpack, and I had the issue before installing that.