Also try to slow the connection down, selecting B instead of G will go from 54 to 11 mbps to see if that help Having your access point support both B and G is very poor practice - it will reduce the throughput for both.
By all means test with one or other (or both), but for normal use it should always be one or the other.
SD
Yes it reduces the throughput of both, and having 11b clients can reduce the number of effective supported 11g clients, but it's not as bad a practice as SD claims. If you have the requirement to support both 11b and g clients, it's acceptable practice.
(having worked for a wireless company with guys who wrote the standards from 2004-2006)