What can be wrong?

I have looked for this guidelines and were hopeful to finally get this multi-site thing working.
Sorry to say I did not.
I get the following message:
PDOException: SQLSTATE[42S02]: Base table or view not found: 1146 Table 'longstay_longstayspain_com.semaphore' doesn't exist: SELECT expire, value FROM {semaphore} WHERE name = :name; Array ( [:name] => variable_init ) in lock_may_be_available() (line 167 of /home/longstay/public_html/includes/lock.inc).
I have only done the first drupal installation on my main domain. I have changed the document root in the Add on Domain in Cpanel to the same root as my maindomain for the second domain.
And of course made the directories and the settings.php.

Would be grateful for some tip of what I have done wrong.



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