license key problem

on all RB150 can update license key

ip address is set , dns is set , router is able to ping www.yahoo.com , or www.mikrotik.com , it resolve host
but when under /system license click update license key it says could not resolve www.mikrotik.com

The router doesn’t need to be connected to the Internet, the computer that Winbox is running on must have Internet access and be able to get to www.mikrotik.com