I have tried all day (literally) to get this working. I am using shared hosting. Tried to read the the forums, checked the web and even had my hosting company try several times (3 tickets) and they get the same errors. This is a powerful tool, but errors are challenging.
Here is my .htaccess code in my admin folder from the main directory like /mynewproject/admin/
# If know that mod_rewrite is enabled, but you are still getting mod_rewrite errors,
# uncomment the line below and replace "/admin/" with your install directory.
RewriteRule !\.(js|ico|gif|jpg|png|css)$ index.php
My index.php file has not changed. I also updated the other two .htaccess files as well. They seem work fine from the browser.
Prior to this, I received the mod_rewrite error as well, so it installed just fine, all PHP tables are fine, but now I cannot login.