Attempt the following:
If you are certain that you have properly installed NI-Serial version 1.6 proceed to step 2.
1.Uninstall your board and any NI-Serial software on your machine, and then reinstall NI-Serial Version 1.6. If you do not have a CD handy, you can download it by selecting Serial, NI-Serial, 1.6, and Windows XP respectively in the drop down boxes at: http://digital.ni.com/softlib.nsf/MainPage?ReadForm&node=132010_US
Reinstall your board after you complete the software installation process.
2. If the problem persists after step 1, go to Device Manager and find your serial ports with exclamation marks. Right click on them and select uninstall. After uninstalling, reboot your machine and let the operating system find them again.
If the pr
oblem still persists, please repost and we will take a closer look!