Please try the following suggestions and try not to overlook on any of these:
You might want to update your Wi-Fi adapter's driver to the latest one by dowloading it from the Manufacturer's site, it might help.
Also, please install and run Xirrus Wi-Fi Inspector
from the problematic computer. Double click the Xirrus Icon on his laptop's desktop, Tap the Printscreen key on your keyboard, open up Paint then choose Edit from the Menu and select Paste, then SAVE it. Upload and attached the file here.
If you are using the Vendor's Wireless Utility make sure that the Windows native Wireless utility is Disabled.
An update will be nice.