I got the error "could not connect to database" when access the database menu (I use enhance skin)
website and phpmyadmin can connect database without problem.
then I select stable channel and update back to 1.660, and can manage database without problem.
I check /usr/local/directadmin/conf/my.cnf and mysql.conf both look ok with correct password.
once update back to 1.661 error "could not connect to database" came back.
now using 1.660 for workaround.