Out of sudden, now new user created cannot login. Error message :
Internal Server Error
The server encountered an internal error and was unable to complete your request.
Please contact the server administrator if this error reappears multiple times and include the technical details below in your report.
I have disabled memcached.locking on config.php and now the login for new user is working fine.
Now this message appeared on my admin setting page. Security & setup warnings Transactional file locking should be configured to use memory-based locking, not the default slow database-based locking. See the documentation for more information.
Is there any negative side affects with disabling memcached.locking ?
the message you have quoted contains a text “See the documentation for more information”. Have you tried to click on that link to see if the mentioned information contains some notes on the side affects?