cadkid says, "I am using A2K but should be the same for A2Ki." I agree that it should be; however, Autodesk didn't see it that way, and thus it isn't the same. You've got to buy Express Tools separately for A2Ki.
Another idea is to make sure that you haven't defined a block using the layer you're trying to delete. If you have, you'll have to redefine the block, changing any of its objects on said layer to another layer. Or, if you're not actually using such a block definition, then you can purge it from the drawing. The layer should then be purgeable as well.
As a test, you can WBLOCK the drawing to another name and see if that gets rid of the layer. If it doesn't, then you probably have an object, even a block as described above still using that layer.