I have the same problem. I’m running 10.5.7 and just installed FCP 6.0.1 in order to work on a project that was started on another system.
I tried to install the 6.0.6 update and get an error message that I need to update from 6.0.5.
I’ve just spent the last hour on-line looking for 6.0.5 and can’t find it.
Any hints? I’m a Avid user so this is all new to me.