Chrome-help. Sidebar under the content, ONLY on index.php

Hiya guys!
I messed up… *blush*

I’ve been working on a theme for a while, and it has worked fine, until yesterday.

In firefox – everything still looks fine!

My address is: https://oursketchbook.com, and if you browse it in CHROME you’ll see that the sidebar is under the content.
If you’ll check the permalink to a post: https://www.oursketchbook.com/kavaj/
It all looks allright, and
If you check my testsite: https://oursketchbook.com/test
it all looks fine

So I must have done something, but I can’t figure out what. I’ve been trying to validate, and fix errors, but it doesn’t help, and I really don’t understant the validator-thingie, becausesome of the errors create new errors if I change them.

I would really appreciate your help, because I think I stared myself blind on all the coding.

Please help!