please make sure that it is using Client Installation Wizard version 1.7.0.1 which contains client radio firmware version 5.60.20,
NDIS driver 8.7 and ACU version 6.6. Using current software enables us to remove the possibility of a previously known and fixed problem from the equation.
Next, make sure that the computer itself is free from viruses and spyware, which may be contributing to the problem. Just because the user of this machine isn't attacking his own network, doesn't necessarily mean that someone from the outside isn't doing so without his knowledge.