Administration - Installation - Core: DB-Error, Upgrade from 4.4

Hello,

I need to upgrade from a ILIAS 4.4 version. First step was to upgrade to 5.0, but in step #4418 the following error is thrown:

PHP Fatal error: ilDB Error: addUniqueConstraint(tst_active)<br />MDB2 Error: constraint violation<br />_doQuery:
[Error message: Could not execute statement]\n
[Last executed query: ALTER TABLE tst_active ADD UNIQUE uc1_idx (user_fi, test_fi, anonymous_id)]\n
[Native code: 1062]\n[Native message: Duplicate entry '13-14-GQYKx' for key 'uc1_idx']\n

How can I fix this ? Any suggestions welcome!

kind regards,
Anton