Not sure if this helps, but I just tried accessing an image here: http://www.bjornvanderhoff.com/wp-content/uploads/1152827983.jpg and it still gives me a 500 error. Does that make any sense?
I fixed it:
In the single.php change
<div id="content" class="widecolumn">
to
<div id="content" class="narrowcolumn">
Then I added the sidebar tag at the bottom.
Thanks guys!
Unfortunately that didn’t work… Any other ideas?