importing texture unity 3.5.1


I have a project done with Unity 3.4.2 and now I converted it to Unity 3.5.1 but some textures failed to import.

I have a few of those textures that I use for particle effects and they only have alfa channel. When I try to import them from the editor gui I get error message:

Failed to execute /Applications/Unity/

Any ideas?

did u ever get a solution for this?