Class 'model_TaskType' not found in 

您应该始终使用精确的大小写.

you should always use exact capitalization.

如果你有 Model_TaskType，添加到 CRUD 时应该是 Model_TaskType.

if you have Model_TaskType, it should be Model_TaskType when added to CRUD.

还有这个地方:

$this->addField('tasktype_id')->refModel('model_TaskType')->mandatory(true);

应该是:

$this->addField('tasktype_id')->refModel('Model_TaskType')->mandatory(true);

在 widows 上，文件名大小写没有区别，而在 linux 中则有区别.

On widows, file name capitalization does not make a difference, where as in linux it does.