So I got the latest 8.1 navi disc today and decided to give my dad my 6.1 disc since he had the 5.1 version. While installing the 6.1 on his car I got an error message that reads unable to read map, Check to see if correct DVD was inserted. And now wont even play his previous disc. Is the CD different for IS models and LX models? Because I know I was able to play GS and RX navi discs on my car but why cant his car play mine?

BTW, our cars are both 2006.

 

It's the wrong generation for your dad's vehicle. Your car has a Gen 5 navigation system, your dad has Gen 4. The LX didn't get the upgrade to Gen 5 until 2007.

 

Yep you cannot swap different Generation navi discs.