Define sediment core error in 2D view plan

Dear all,
I have define sediment core in 2D view plan, but there is error. The error message are "can’t preserve array! resetting ! run time error 91: object variable or with block variable not set. In the first, I tried to use “define new core in 2D view plan”, successfully.
How to get the true “define new core” ?

We think the problem is that you are trying to edit the sediment cores before you have defined your sediment classes and properties. You must define your sediment classes before proceeding to this sediment core tool.