I think Giomen is on to something there, the GPSMAP 276c is not in the compatible devices list for BlueChart g2:
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Nor are BC g2 in the maps list for the device itself:

gpsmap276c

But the 3rd party CCD Gold should still work ok.

I doubt the firmware was updated by Garmin to increase its capability beyond the old original BlueCharts as Giomen is suggesting:
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However, there was a firmware update to v5.70 about 18 months ago in May 2013, so it you haven't updated your unit recently you could try that MarianoDC.
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