Replacing the laser mechanism is very easy, but not guaranteed to make a difference on reading an aftermarket dvd (in my experience). However, since the original poster's factory nav dvd can't be read, then it is probably the dvd laser issue.

It takes 10 minutes to do once you have the T9 torx and jewelers flat blade screwdriver in your hands and the nav drive on your workbench (or, in my case, living room coffee table).

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual