Hi,
Most likely, you either have not installed the Web Player or better on the client machine (use the link on the page that appears), or you don't have permission on the server. There are some other scenarios also. Take a look here..
http://digital.ni.com/public.nsf/websearch/BE15FB343C2E9BA4862569DC007AC900
Good Luck...I still don't have this working as it should. I get a kick out of this from NI in 2001...Quote "Note: National Instruments is working on Lookout Web Client fixes and improvements to make the whole process smoother."
Haven't seen "smooth" yet!
Ed