I agree with kknigga...

The thing to look at is the permissions on the .ssh directory and the known_hosts file. Try a simple test like:

(as ngtman)

echo "test" >> ~/.ssh/known_hosts

Now edit that file and see if the word "test" is at the end of the file.

If it is your permissions are fine, remove the "test" line and save the file again.

If it isn't you have a permissions issue.