AssetDatabase.ImportAsset fails on generated textures

I'm trying to generate a number of PNG icons from 3d objects in Unity. Generating and saving the images works fine, but I can't seem to finish the process of saving the new assets to the database. When I attempt to use AssetDatabase.ImportAsset(), it fails with the following error:

 Could not create asset from Assets/Artwork/Resources/Icons/Insertions/Carnation - Light Blue.png: Texture could not be created.
 UnityEditor.AssetDatabase:ImportAsset(String, ImportAssetOptions)
 Editor.IconGenerator:SaveTextureToPNG(String, Texture2D) (at Assets/Code/Editor/IconGenerator.cs:95)
 Editor.IconGenerator:GenerateInsertionIcons() (at Assets/Code/Editor/IconGenerator.cs:38)
 Editor.IconGenerator:GenerateAllIcons() (at Assets/Code/Editor/IconGenerator.cs:17)

That path is directly from a previous reference to the asset, so I don't understand why it fails. When I check in the inspector, the new assets exist, and the settings are actually changed, but they haven't been applied.

Here's a snippet of the larger script:

 TextureImporterSettings settings = new TextureImporterSettings();
 settings.alphaIsTransparency = true;
 settings.alphaSource = TextureImporterAlphaSource.FromInput;
 settings.sRGBTexture = true;
 textureImporter.SetTextureSettings(settings);
 EditorUtility.SetDirty(textureImporter);
 AssetDatabase.ImportAsset(path, ImportAssetOptions.ForceUpdate);