Please read my post here: http://community.crutchfield.com/forums/p/22187/251957.aspx (pasted below).
I hope you bought your unit at a Clarion dealer....
Hi, (Team Crutchfield - please add this to your knowledg-base.)
I'm on my third NX501 (could have been the fourth if not for working directly with Clarion).
The SD Card corruption causes both loss of Navigation and intermittent Sirius start up (it'll never acquire signal).
Your unit needs to use the exact micro sd card it came with forever (it has a permanent serial number).
You have two choices:
1. Get Crutchfield to replace the unit
2. Call Clarion (I suggest this rather than ripping your dash apart over and over).
Here's what to do. Contact:
Customer Service Technical Representative
Clarion Corporation of America
800-347-8667 ext 4342
Direct Line: 310-217-4342
Ben will have
you send your microsd and rebuild it for you and return it (likely with
the firmware upgrade that addresses this issues on another microsd that
can also be found here:
While you're at it, update the Bluetooth firmware too: http://www.clarion.com/us/en/support/software/NX501/index.html
Once you get
the card returned (THIS IS HUGELY IMPORTANT - EVERYONE WITH A Clarion
NX501 SHOULD DO THIS!!!), back it up using Naviextras toolbox (the
program clarion uses for map updates). You can get it here:
follow these steps, barring your micosd physically or logically self
destructing, you'll have an NX501 that's nearly problem free and backed
up just in case that unfortunate corruption reoccurs.
Of Note: Ensure you insert the microsd card with the contacts facing up and do not force anything.
confident this will make a world of difference for you (and anyone
suffering the microsd corruption of the Clarion NX501).