Duplicate entry '' for key 'username'

Hello,

When I try to add a new backend user I get this error:

Fatal error: Uncaught exception Exception with message Query error: Duplicate entry '' for key 'username' (INSERT INTO tl_user (language, showHelp, thumbnails, useRTE, useCE, inherit, alpty, fop, tstamp) VALUES ('sv', 1, 1, 1, 1, 'group', 'a:3:{i:0;s:7:\"regular\";i:1;s:8:\"redirect\";i:2 ;s:7:\"forward\";}', 'a:3:{i:0;s:2:\"f1\";i:1;s:2:\"f2\";i:2;s:2:\"f3\" ;}', 0)) thrown in system/modules/core/library/Contao/Database/Statement.php on line 282
#0 system/modules/core/library/Contao/Database/Statement.php(253): Contao\Database\Statement->query()
#1 system/modules/core/drivers/DC_Table.php(640): Contao\Database\Statement->execute()
#2 system/modules/core/classes/Backend.php(424): Contao\DC_Table->create()
#3 contao/main.php(129): Contao\Backend->getBackendModule('user')
#4 contao/main.php(276): Main->run()
#5 {main}

What does it mean and how do I fix it?
Thankful for all help!

Quote:

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Duplicate entry '' for key 'username'

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It looks like the User allready exists?! Did you try a other username? Or just put a number in the end of the Username to see if it is a duplicate name.

Hi,

i can reproduce the error in a test environment.

- I modified my DCA definion of the field 'username' in tl_user (deleted the eval-Array, so the field is not mandatory).
- Then i added a new user with an empty username
- Adding a second new user is impossible ... i get the same error like the one above

So, check your database table 'tl_user' for an empty 'username' and put in a value.
And check the dca config. Be sure 'username' is mandatory!

Greetings, Cliff