No gremlins.....
You have to program both keys at the same time
When coding keys to the car the memmory is erased, so if you code one key then only that key wil work.
Just do the coding for the both keys at the same time and it wil be fine

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X5 4,4i-06 Current
330Ci Cab-03 2007-2008
MB E55 AMG-03 2006-2007
Z3 2,8 Roadster-98 2006-2007
X3 2,0d-05 2005-2006
320d-99 1999-2005