I have an '03 4.6 that refuses to take a navigation disc newer than what came in it (2003.2, I believe). I tried the 2005.2 and 2004.2 discs, but the display read something to the effect of "Invalid navigation disc in drive." Are all X5s supposed to be upgradable? The dealer said something about a difference between green and blue discs... They'd had success with one but not the other. Any ideas?