Piwik version 1.8.3. Database version MySQL 5.x
For new users, who doesn't have any existent dashboards in a database table prefix_user_dashboard, attempt to create a new dashboard leads to an error.
Piwik_Dashboard_Controller::createNewDashboard method has sql query (183 line of the file) 'SELECT MAX(iddashboard)+1 FROM '.Piwik_Common::prefixTable('user_dashboard').' WHERE login = ?". Unfortunately this returns NULL value, when table doesn't have any records by this conditions. After that we are have a next query on line 194, which throws an error, when receives a null-value in $nextId variable.