Database Error: Can’t Login anymore / Redirect to Login Screen

Hi,

on one of my websites I could not login anymore and always was redirected to the login screen. After turning on the Debug mode, I get following error.

I could be, that it occured after an update to 4.6.4.

Any ideas how to solve it?

Thanks in advance

Charly

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Error Description:

WordPress-Datenbank-Fehler: [INSERT command denied to user ‘web666’@’localhost’ for table ‘wpart_options’]
INSERT INTO wpart_options (option_name, option_value, autoload) VALUES (‘_transient_doing_cron’, ‘1489395081.1021549701690673828125’, ‘yes’) ON DUPLICATE KEY UPDATE option_name = VALUES(option_name), option_value = VALUES(option_value), autoload = VALUES(autoload)

Warning: Cannot modify header information – headers already sent by (output started at /var/www/web666/html/wp-art/wp-includes/wp-db.php:1401) in /var/www/web666/html/wp-art/wp-login.php on line 402

Warning: Cannot modify header information – headers already sent by (output started at /var/www/web666/html/wp-art/wp-includes/wp-db.php:1401) in /var/www/web666/html/wp-art/wp-login.php on line 415

Warning: Cannot modify header information – headers already sent by (output started at /var/www/web666/html/wp-art/wp-includes/wp-db.php:1401) in /var/www/web666/html/wp-art/wp-login.php on line 417