Problem when posting a story

I just recognized a problem regarding story posts...

When i write linux commands in a story i get an error:
Forbidden
You don't have permission to access /drupal/node/27/edit on this server.

I use FCK editor plugin but also with plain text input the same happens.

F.e. if i type in a story:
wget http://somepath
and save the story i get the error written above...

using
wget_http://somepath
works...

I still use drupal 6.6 and mod-rewrite in php...

Maybe anyone has an idea?
Thx!