Can't add a parent to a existing list
I am having some troubles adding a new hierarchical level to an existing list, which is called BU01 Business Unit and it's not a numbered list; the new parent should be BU00 Business Unit Combine:
If I try to compile the parent hierarchy column, I get this error:
If I try to delete All Business Unit from the Top Level column, I get this other error:
How can I solve this issue?