Asset bundle creation

Trying to create a asset bundle by following these directions(https://docs.unity3d.com/550/Documentation/Manual/BuildingAssetBundles.html) but get this error.
AssetBundle names "structures.1" and "structures" can't exist in the same build as "structures.1" has the variant.
UnityEditor.BuildPipeline:BuildAssetBundles(String, BuildAssetBundleOptions, BuildTarget)
CreateAssetBundles:BuildAllAssetBundles() (at Assets/!!0myscripts/Editor/CreateAssetBundles.cs:8)

Code (CSharp):

1. using UnityEditor;
2.  
3. public class CreateAssetBundles
4. {
5.     [MenuItem ("Assets/Build AssetBundles")]
6.     static void BuildAllAssetBundles ()
7.     {
8.         BuildPipeline.BuildAssetBundles ("Assets/AssetBundles", BuildAssetBundleOptions.None, BuildTarget.StandaloneOSXUniversal);
9.     }
10. }
11.  

 

For anyone who gets here from Google: if you have a bundle without a variant ("structures"), you can't also have one with a variant ("structures.1").

You'll need to make "structures" be "structures.default" or something so they both have a variant set.