There are some default attributes that can't be deleted.
They can be re-named however which it looks like has happened in your case as I don't believe this is a default line type name.
You may find if you go in to the Attribute Manager, you may be able to delete that line there if you really need to.
If it has a tick next to its name in attribute manager, then it is being used somewhere, so best not to delete it.
As far as I know the only line you definitely can not delete is the solid line (attribute number 01).
Barry.
One of the forum moderators.
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