Facebook – Is Username Retained When Converting Profile to Page?

Make sure you have already "liked" the page you wan't to link to. it should work after that..it works for me. but I am a page administrator...so...that might also have something to do with it

In addition to the answer provided by Chris, an easier way to get your ID is to enter the URL:

https://graph.facebook.com/{YOUR_FACEBOOK_USERNAME}

This will provide you with your ID which you can use with the URL as mentioned by Chris.

http://www.facebook.com/profile.php?id={YOU_FACEBOOK_ID}