Facebook and Friend Requests?

I use to be able to send out as many friend requests as I wanted like on MySpace. But now I can send out 4 or 5 and then it blocks me or something. It happens with certain people, I'm unable to add people I work with but the friend requests go through with other people. Almost like there is a trick to it, for example I can't add Steph M, Sherry S, Tim V or any of the people I work with but requests go through with people from high school. So there might be some way to fix it by adding more schools to my profile. Because Facebook has been "Broken" for the last 3 months saying "Do you know this user personally?" 80% of the time I go on.