When having many Limesurvey installations on the same server and you want to add another fresh installation you really have to take care to use the correct settings in config.php. Otherwise you might update an existing installation instead of setting up a new one because when calling /admin/install the update script is called automatically without asking you if you really want to proceed. You might end in having an old installation using old files but being updated to the latest DB scheme which causes lots of problems at this old installation.