License Key stop working after a few minutes

[TabuNuf]

And before you think - well that is a pirated license key, then no, its a key that was purchased.
I have used this on a few different computers over the years, but this time I switched to a mac, and now the key is accepted, but after a few minutes, it tells me " Your license key is no longer valid, and has been removed "
Do I need to purchase a new key, did I use it on too many computers?.. or what is going on?