Products purchased from the asset store are also distributed by the asset store (outside of my control) and their delivery process has issues from time to time.

A quick search of Google with show that people have been having this issue for years and I am surprised that Unity has not implemented a better distribution system by now.

So - the quick set of things to check for are:

  1. You try it install your package and fails. Does your target disk have enough space to decompress the package?
    FIX: Create more space on your target disk - you need at least twice the free space of the original package for this to complete properly.

  2. Does your Unity Project or UnityPackage exist in a directory with non-English characters in it?
    FIX: Remove the non english characters.

  3. Do you have read\write access to the UnityPackage, its parent directory, and your Unity Project's directory?
    FIX: Fix up your permissions.

If you are still having a problem then please lodge a support request with Unity at