I just encountered this problem for the first time - I was trying to update “Master Audio” from the Download Manager menu and after it was downloaded, an error message pop up saying “NOTHING TO IMPORT !”. I checked the file version it still says v1.4 (current version is 1.5). I then went back to Asset Store main menu and download Master Audio from there and this time the import menu finally pops up and allows me to import. After importing I checked the file version it is indeed v1.5. I am currently on Unity 3.5.7.
I’m having this issue with my own asset. I can’t update it since November/2012.