Repair  "Add effort not working"

After click Button Add effort flypray generate PHP error: 
flyspray\index.php:169 0.1238 5969864 3. effort->addEffort() 
modify.inc.php:383 Query {INSERT INTO `flyspray_effort` (task_id, date_added, user_id,start_timestamp,end_timestamp,effort) VALUES ( ?, ?, ?, ?,?,? )} 
with params {,1412929715,1,1412929715,1412929715,36000} 
Failed! (Column 'task_id' cannot be null)