Free Accounting Software

Users can't register

Your issue is related with the Access Level of the menu item that the user SEF URL is using. You should have a record like the following Real URL in AceSEF=>URL section:

index.php?option=com_user&Itemid=20

This is the page that Joomla redirects you just before finalizing the registration process but the menu item with the ItemID #20 is viewable only by Registered users.

You should set the index.php?option=com_user (without Itemid variable) as Used.

If you're using Community Builder then you should modify the Itemid value of the record that has task=registered in the Real URL with a Public Access Level Itemid.