We've noticed a strange situation with some users:
they install Unity Webplayer as part of registration process for our web game, but the browser doesn't detect the installation successfully completing as it should.
We can't reproduce it, but seems the only common scenario is that they have Vista and Internet Explorer
Anyone else seen similar?
I just downloaded unity Player for IE 8.0.6001.18904 for vista and no problem. I use chrome and safari usually. You need more data about their OS and browser.
Check if the system has UAC enabled and the browser is running in the protected mode.
From what I recall that can have a negative impact as that mode kills quite a bit of "outer world interaction" it considers "not as save as I want it to be"