Questions Selector Type attribute cannot delete in acumatica

Hi All,

Just wanna ask if there is a way to delete this selector type attribute.

As you can see, there is an error saying the attribute does not exist. But when I check my attributes, it exists. I also trace if there is some data on my project, and since it is a required field, the system does not allow me to leave them blank when saving my Projects. Even I uncheck the Required field, it still gives me the same error as above.

Here is my attribute for that. I think this is related to the Selector type of Attribute.