It might help if we knew which wireless chipset your card uses:
from a command prompt will probably tell us that, and what method of driving the card you are using. Native Linux driver or ndiswrapper.
There are two other possibilities I can think to check. Firstly not all linux drivers are happy with the "draft n" capability turned on in an access point and secondly, not all linux drivers are constructed to use all the channels available in all parts of the World. As an instance, in Europe we can use channels 12 and 13 in our Access points but some Linux drivers seem not to work with them.
Might be worth experimenting with.