Error importing folder: pathName already mapped?

Sometimes when importing an asset I’ve created or exported as a .unitypackage I see this error:

Error importing folder (The pathName [some path] is already mapped to [some hash]. But the meta data wants it to be mapped to [some other hash])

Does anyone know the cause or how to fix/prevent the problem?

It happened to me once only but I have no idea why or how it happened. I think it happened after I upgraded a u4 project to u5 then later tried to reimport the asset that was imported during u4. I think so… Like I said, it only happened once.

The only thing I can think of is that perhaps you have two kits that share the same folder/scripts like for instance two assets that create the Assets/StandardAssets folder but in one package the UID for the folder is one value while in another it has another value so when it tries to create the same path twice it goes “Hold on a minute…! What’s this?”

That’s the only reason I can come up with for this happening…