The Planned Start/End date on child project task does not roll up to the parent project/project taskIssue Project task doesn't allow for start date to be earlier than project start date.ReleaseParisCauseProjectWorkbenchPhaseValidationAndUpdate Business Rule customizedhttps://instancename.service-now.com/sys_script.do?sys_id=85005e90d713210058c92cf65e6103cf And the following sys_ui_message is responsible to display the error message --> 'Project task "Planned start date" cannot be prior to the parent task'https://instancename.service-now.com/sys_ui_message.do?sys_id=52abcfe30f9ee20080daad7d51050e2dResolutionRevert above to OOB version(s)Or, adjust the Business Rule according to business needs