This error occurs when AssetDatabase.LoadAssetAtPath is called on a file. It also occurs when the file is selected in the project window.
In the situation I am seeing, it occurs with a .anim file that is stored in the YAML text format.
Is this a custom editor script you’re having trouble with? If so, you might make sure that the asset you’re trying to manipulate is one that you’re able to use in the editor normally, and that you’re using a valid path that points to a real asset of the type you’re expecting.
Otherwise, you might want to make sure that you have appropriate permissions to access that file. Does it exist? Can you open the file in a text editor like Notepad++? Is it possible that another program is editing the file currently? Could you try re-importing the asset?
Try to check all yours .meta files for svn or git conflicts. Sometime it cause that type of error.
Here is description and script to fix similar problem. Maybe it will help in your case.