500 Internal Server Error

Hi,

I tried changing the htaccess file by redirecting http://mydomain.nl to http://www.mydomain.nl since it is better for SEO to have all traffic to one domain. Now I get the following error:

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator to inform of the time the error occurred and of anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

I already changed the htaccess file with the old one but that did not help. All the pages are not available anymore. Hope to receive some help so that my website is accessible again soon!

Cheers

edit: I fixed it so the website works again. Now I just want to make sure that I do not have two seperate domains for SEO. One should direct to the other. How can this be done in the htaccess file correctly?