Tom Usher commented or added the following:
Why didn't my friend request go through?
Facebook is a place for connecting with friends, family and other people you know personally.
If you've been prevented from adding friends on Facebook, it's likely because many friend requests you've sent recently have gone unanswered. This may be because you've sent friend requests to strangers, or it may be due to other behavior that Facebook members have reported as unwelcome.
You'll be allowed to add friends again soon. At that time, please remember to only send friend requests to people who you already know personally. Otherwise, additional limits may be placed on your account.
For more information on your rights and responsibilities as a Facebook member, please click "Terms" at the bottom of any Facebook page.