Force to www WordPress SEO

I had a previous run in with jquery error which has been solved. However, I discovered that if you go to mydomain.com the error is back.

This is caused by juuery thinking its cross domain.

So, I changed my WP admin to http://www.mydomain.com.

I also made http://www.mydomain.com the Google preferred domain long ago.

The first time I went to mydomain.com it brought up http://www.mydomain.com and I assumed the issue was solved.

But it stopped forcing to www. When I try it now, it stays mydomain.com and errors.