SOLVED!
After researching the problem I found that somehow my mysql.sql_mode was set to: ONLY_FULL_GROUP_BY,NO_AUTO_VALUE_ON_ZERO,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
I have no idea why, no one should have...