Found the problem and I have a solution.

This line (line #262) in include/common.php is emptying the user info:
// Remove expired session for xoopsUserId
if ( $xoopsConfig['use_mysession'] && $xoopsConfig['session_name'] != '' && !isset($_COOKIE[$xoopsConfig['session_name']]) && !empty($_SESSION['xoopsUserId']) ) {
unset( $_SESSION['xoopsUserId'] );
}

For some reason, right after the login, I suspect the cookie to contain the wrong info, thus preventing anyone from login anymore.

I commented out the line #263 (the unset()) and everything is back to normal!

Hope this is useful.
Ben

I have the solution.

This line (line #262) in include/common.php that was emptying the user info:
// Remove expired session for xoopsUserId
if ( $xoopsConfig['use_mysession'] && $xoopsConfig['session_name'] != '' && !isset($_COOKIE[$xoopsConfig['session_name']]) && !e
mpty($_SESSION['xoopsUserId']) ) {
unset( $_SESSION['xoopsUserId'] );
}

For some reason, right after the login, I suspect the cookie to contain the wrong info, thus preventing anyone from login anymore.

I commented out the line #263 (the unset()) and everything is back to normal!

Hope this is useful.
Ben

Also found this line (line #262) in include/common.php that was emptying the user info:
// Remove expired session for xoopsUserId
if ( $xoopsConfig['use_mysession'] && $xoopsConfig['session_name'] != '' && !isset($_COOKIE[$xoopsConfig['session_name']]) && !e
mpty($_SESSION['xoopsUserId']) ) {
unset( $_SESSION['xoopsUserId'] );
}

For some reason, right after the login, I suspect the cookie to contain the wrong info, thus preventing anyone from login anymore.

I commented out the line #263 (the unset()) and everything is back to normal!

Hope this is useful.
Ben