I started by commenting all lines in the .htaccess file (that werent already commented). tested the site and it loaded up. Then one by one, uncommented the lines and tested the site.
When I uncommented this line...
SetEnv HTTP_MOD_REWRITE On
I got the error again. I commented it back, and checked the rest, uncommenting and refreshing. All is fine. Its just this one line. I also tried it as 'Off' but got the error again.
So now the site loads. I can access the login page, but I cant login. It doesn't accept the password I set up when I did the local install.
JohnHalsey's post in Error when uploading local MAMP site to live was marked as the answer