Bug in Calendar_DetailRecordStructure_Model
In a recent commit, you removed the method setupAccessiblePicklistValueList() from within the Calendar_DetailRecordStructure_Model expecting it to be using the inherited parent.
Unfortunately the parent function in Vtiger_DetailRecordStructure_Model expects to be passed a Field_Model whereas the original method in Calendar_DetailRecordStructure_Model was passed the field name:
$this->setupAccessiblePicklistValueList($fieldName);This no longer works and if you log in as a non-admin user, you get a white-screen-of-death when trying to access a Calendar record in Detail View.
You need to change this call: