First, check to make sure you've only entered your LinkedIn username in the field on Working Not Working. The site will autofill http://linkedin.com/in/
If that doesn't work it's most likely you have not set up a public profile on LinkedIn. If you do not have an /in/ URL, you have not yet created a public LinkedIn profile. Here's how to do it:
You can customize your public profile URL when you edit your public profile. Custom public profile URLs are available on a first come, first served basis.
Move your cursor over Profile at the top of your homepage and select Edit Profile.
You'll see a URL link under your profile photo like www.linkedin.com/in/yourname. Move your cursor over the link and click the Settings icon next to it.
Note: "Update your public profile settings" will show up if you don’t have a public profile. Learn how to enable your public profile.
Under the Your public profile URL section on the right, click the Edit icon next to your URL.
Type the last part of your new custom URL in the text box.