Hi There,
Are you using Mac or PC?
If PC then is your username of windows account has spaces in between like, "John Dow"? If so then can you try to use an account with no spaces eg: "JohnDow" and then open the captivate from that account to preview a project.
else if you are using Mac can you check that are you using any proxy in your web server.
Let us know your comments.
Regards
Shriyansh
Adobe Engineering Team