I am also having this same problem with my Black version. I have set up all the parameters correctly, making sure to generate the code for Black and not Black 2. I know for sure that my cartridge is working properly because I had input a different AR code to receive a different poké I had found online, and that worked perfectly. I believe it is the AR code generator on Pokégen.
Here is the Code I have been trying to enter (I want my Butterfree):
94000130 FFFB0000
B2000024 00000000
E0000D20 00000088
EA050ADC 69CC0000
B585C07E 8858489C
06675970 0E2D3E53
A971B05C 5254F7CE
0B4E29CF A5EB7E62
C6934A1B 3AA6C71A
E33D1262 BD5F5EAB
74B45C63 558B99FA
64CAF13E EC4A63B8
4E5860E1 E7570B34
29567633 5980D0C4
BC728C6A D7BD947F
42557AF9 3A6F55E2
6668AF2A 02E13E40
12A04681 C89AA32F
8BDAD1E1 E4093128
5CD903FC EDEA5A94
D2000000 00000000
Game language - English
Box/slot used - B1 S1
Activation button(s) used - Select
Which target game was selected - Black
