Getting error while accessing Gantt

Hi,

I have updated old version to new version projeqtor6.3.4.Iam getting error while accessing Gantt.In the old version also I found same issue.How to solve this.

Hi,

Logs are recorded like this.

2017-08-29 17:31:12.551 ===== TRACE ===== NEW CONNECTED USER 'admin'
2017-08-29 17:38:25.071 ***** ERROR ***** [V6.3.4] Impossible to load class WorkElementType<br/> => Not found in ../model/custom/WorkElementType.php <br/> => Not found in ../model/WorkElementType.php <br/> => Not found in ../model/persistence/WorkElementType.php <br/>
2017-08-29 17:57:12.032 ***** ERROR ***** [V6.3.4] ERROR *****
2017-08-29 17:57:12.045 ***** ERROR ***** [V6.3.4] on file 'C:\xampp\htdocs\projeqtor1\tool\jsonPlanning.php' at line (517)
2017-08-29 17:57:12.049 ***** ERROR ***** [V6.3.4] cause = Undefined property: PeriodicMeeting::$idPeriodicMeetingType