Lansweeper scans license keys as and if they are stored in the registry of your network computers. For MAK (Multiple Activation) keys in particular, Lansweeper will not be able to scan them as they are not stored in the registry. Lansweeper is showing you an informational message that the machine is using a MAK key, but that the key itself cannot be recovered. Unfortunately, there is currently nothing we can do about this issue as this is how Microsoft uses MAK keys.
As this has been asked by our customers before, the ability to recover MAK keys if possible is currently on our customer wish list. I've moved your post to the wishlist section in this context. Unfortunately, we are unable to provide you with an estimated release date for when/if this might be implemented in a future Lansweeper release.