We are in the process of implementing NAC and using the ActiveX page to refresh the ip address of the user. We have been testing with Windows XP and not found any issues. We have discovered that Windows 7 machines have an issue with the refresh of the ip address after the authentication has occured. We have tested with the same switchport on two different machines and the XP machine works without issue. The Windows 7 machine will 3 time out of 5 bring up a dialog box stating that the user needs to Refresh the IP address. A ipconfig /release and ipconfig /renew works and the machine gets the correct ip address. Is there something that needs to be done to correct this issue? Spanning tree portfast is configured on the port.